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The amino acid sequence of the first domain (positions 1·175) of Panulirus interruptus hemocyanin subunit a has been determined. The sequence of residues 1·158 (18-kDa fragment obtained by limited proteolysis) was derived from peptides obtained by digestion of this fragment with CNBr and trypsin and by subdigestion of these peptides with other enzymes. The peptides were sequenced automatically or manually. The amino acid sequence has been fitted into the electron-density map at 0.32-nm resolution. The residues of domain 1 are folded into a larger, mainly helical, globular part, containing one disulfide bridge, and a smaller part near the molecular twofold axis. The latter part consists of an α helix and a β strand which contains a covalently attached carbohydrate moiety. The sites susceptible to limited proteolytic cleavage of the subunit are discussed. Comparison of the N-terminal sequence with those of other arthropod hemocyanins revealed, besides an N- terminal extension of five residues, the presence of a 21-residue loop (positions 22–42) in the crustacean sequences. This loop contains helix 1.2, a less defined region in the electron-density map. It is absent in chelicerate sequences. Strong evidence is presented that: (a) the structure of the first 21 residues (including helix 1.1) is the same in all arthropod hemocyanins with known amino acid sequence; (b) a stretch containing about 15 residues (including part of helix 1.3) following the 21-residue loop has a different structure in crustaceans and chelicerates; (c) the rest of domain 1 has the same structure again. It is shown that all conserved residues are in the contact region with the other two domains. [ABSTRACT FROM AUTHOR]

Limited proteolysis of the native monomeric 94-kDa subunit of Panulirus interruptus hemocyanin by trypsin, plasmin and subtilisin produces an 18-kDa fragment. a 71-kDa fragment and a small glycopeptide. In the plasmin digest a 23-kDa precursor of the 18-kDa fragment has been observed. Automatic Edman degradations demonstrated that the 1 8-kDa fragments have their origin at the N terminus of the 94-kDa subunit and incubations with carboxypeptidase A showed that the 71-kDa fragments originate from the C terminus. The glycopeptide is situated in between. The amino acid sequence of the glycopeptide has been determined, its carbohydrate content accounts for the total carbohydrate of the 94-kDa subunit. All three proteases cleave the subunit at two positions within a very restricted area of the polypeptide chain. which indicates the presence of an exposed loop, carrying the carbohydrate chain, in the corresponding part of the native molecule. [ABSTRACT FROM AUTHOR]

Arterial levels and cardiac and hepatic arteriovenous differences (AVD), extraction coefficients and oxygen extraction ratios of glucose, lactate, pyruvate, free fatty acids, acetoacetate, 3-hydroxybutyrate, citrate and oxygen were determined simultaneously by catheter techniques in anaesthetized (chloralose­urethane) normal, and in acute and chronic alloxan­diabetic dogs. The differences in mean values between the normal and the diabetic groups were tested for their significance by analysis of variance and the dependence of AVD values on their corresponding arterial levels by correlation analysis. The arterial levels of glucose, free fatty acids, acetoacetate and 3-hydroxybutyrate were significantly raised in both diabetic groups. Citrate was significantly elevated only in the acute diabetic animals. Arterial pyruvate was significantly lowered in both diabetic groups. Arterial pH values of around 7.24 were found in the acute diabetic animals. Cardiac AVD of glucose was significantly reversed in the acute diabetic dogs. The myocardial AVD of pyruvate and lactate were positive in normal, and significantly negative (except lactate in chronic diabetes) in both diabetic groups. A significant, positive correlation between myocardial AVD and arterial levels was obtained for lactate in the normal group and for pyruvate in normal and diabetic animals. Arterial lactate/pyruvate ratios were significantly correlated to arterial lactate and pyruvate levels in the diabetic animals. Myocardial AVD and oxygen extraction ratio values of free fatty acids were not significantly changed in the diabetic groups, but myocardial free fatty acids extraction coefficient values were significantly reduced. The myocardial AVD and oxygen extraction ratio values of acetoacetate and 3-hydroxybutyrate were significantly increased in both diabetic groups. A positive correlation between AVD and the corresponding arterial levels of free fatty acids and acetoacetate was obtained in normal dogs. Myocardial citrate AVD and oxygen extraction ratio were significantly raised in the acute diabetic animals. The hepatic AVD of glucose, lactate and pyruvate were negative (release) in normal animals. No significant change in hepatic glucose AVD was found in the diabetic animals, yet the hepatic AVD of lactate and pyruvate became significantly positive (uptake). A highly significant, positive correlation between hepatic AVD and the arterial level of pyruvate was obtained in normal and in diabetic animals, the regression line of the diabetic animals being shifted to a 10-fold lower range of arterial levels. The hepatic AVD of free fatty acids was significantly raised in the acute diabetic dogs and significantly correlated to the arterial free fatty acids level in normal and diabetic animals, with almost identical regression lines. The hepatic AVD of acete­acetate and 3-hydroxybutyrate were negative in all animals but significantly more negative in the diabetic groups. A positive, significant correlation was obtained between AVD and the arterial level of acetoacetate in normal dogs and between the hepatic release of ketone bodies and the hepatic uptake of free fatty acids within all groups. The mean values of hepatic AVD of citrate were negative in all groups, the most negative values being found in the acute diabetic animals. The hepatic oxygen AVD was significantly doubled in the chronic diabetic group. [ABSTRACT FROM AUTHOR]

The primary structure of subunit b of Panulirus interruptus hemocyanin has been derived from two digests (trypsin and CNBr) and, in some cases, with aid from the similarity with the sequence of subunit a. Differences between the amidation states of Asx and Glx residues in subunit b relative to a were investigated more thoroughly. When compared to the sequence of subunit a, 18 differences (2.7%) were found and certain heterogeneities, indicating the presence of a minor subunit b', were observed. Several differences in properties between subunits a and b, including their anomalous behaviour on SDS/ polyacrylamide gel electrophoresis, could be explained by amino acid replacements. [ABSTRACT FROM AUTHOR]

The signal transducer and activator of transcription (STAT) proteins have initially been described as cytoplasmic proteins that enter the nucleus only after cytokine treatment of cells. Contrary to this assumption, it was demonstrated that STATs are constantly shuttling between nucleus and cytoplasm irrespective of cytokine stimulation. This happens both via carrier-dependent as well as carrier-independent transportation. Moreover, it was also recognized that cytokine stimulation triggers nuclear retention of dimeric STATs, rather than affecting the rate of nuclear import. In summary, it is increasingly being appreciated that STAT nucleocytoplasmic cycling determines the quality of cytokine signaling and also constitutes an important area for microbial intervention. [ABSTRACT FROM AUTHOR]

Investigates the trifluoroethanol-induced step-wise folding of helical segment from scorpion neurotoxin. Use of CD and nuclear magnetic resonance spectroscopy in the study; Stabilization of helical segment; Percentage of trifluoroalcohol for the propagation of helix to N and C termini; Formation of helix in the peptide.

Examines the glutamine synthase expression in perinatal spiny mouse liver. Increase of protein to messenger RNA ratio of ammonia-metabolizing enzymes; Kinetics of glutamine synthetase protein accumulation; Role of tissue-specific enzymes in the developmental process.

In the rat intestine, UDP-glucuronosyltransferase (UGT) isoforms were highly induced by oral administration of 2-naphthoflavone, as shown by intestinal UGT activity toward 1-naphthol (1-NA). The greatest increase in UGT activity occurred in the duodenum. Using UGT1A6 cDNA as a probe, we obtained three types of clones corresponding to UGT1A2, UGT1A6 and UGT1A7, in a ratio of 1 : 1 : 8, from a cDNA library constructed from the 2-naphthoflavone-treated rat intestine. The induction of each isoform was evaluated by means of Northern blotting with isoform-specific probes. The mRNAs of UGT1A6 (glucuronizing various phenolic xenobiotics) and the mRNAs of UGT1A7 (glucuronizing the ultimate carcinogenic metabolite of benzo(a)pyrene) were expressed constitutively and were highly induced in the duodenum and proximal jejunum. S1 mapping showed that induction of the isoforms of the UGT1 family was more pronounced in the liver than in the small intestine and that UGT1A7 was the major UGT1 isoform in the small intestine of vehicle-treated rats and in that of 2-naphthoflavone-treated rats. These results indicate that, in rats, UGT1A7 is expressed constitutively and is particularly inducible in the small intestine. In the light of these results, we believe that the UGT1A7 isoform would play an important role in glucuronidation in the small intestinal mucosa of rats. [ABSTRACT FROM AUTHOR]

Structure of growth-hormone receptor and the class I type of cytokine receptors : common structural features; cytokine-receptor isoforms; oligomerization of receptor components initiates cytokine signalling. Role of the Jak kinases in mediating specific functions of growth-hormone receptor and cytokine receptors. Role of signal transducer and activator of transcription (Stat) proteins in growth hormone and cytokine functions. Other pathways activated by cytokine receptors : the mitogen-activated protein kinase pathway; insulin-receptor substrates 1 and 2 and phosphatidylinositol-3-kinase pathways; the Src pathways and other tyrosine kinase pathways; the phospholipase C/protein kinase C/Ca2+ pathways. Regulation of growth-hormone receptor and cytokine receptor signaling : binding sites, internalization and ubiquitination; phosphatases and Janus kinase/Stat inhibitors. Conclusions and future prospects. [ABSTRACT FROM AUTHOR]

Northern blot analysis of bullfrog tissues using a cDNA probe of cytochrome P450(11β) showed that a large amount of message was present in the ovary as well as in tee adrenal tissue. Two kinds of mRNA of different sizes were found in the ovary. Sequence determination of the two cDNAs and analysis by reverse-transcription polymerase chain reaction indicated that the protein encoded by the larger mRNA was identical to the adrenal enzyme, while the protein encoded by the smaller had a truncated sequence lacking an extension peptide necessary, for the protein transport to the mitochondria. The mRNAs were present in the oocytes but not in the follicular cells, and their content in an oocyte varied little during its maturation. Immunoblot analyses of the mitochondrial fraction of oocytes failed to demonstrate the presence of P450(11β) protein. In contrast the eggs were found to contain a large amount of enzymatically active protein. Interestingly the mRNA has a cis-element called cytoplasmic polyadenylation element at its 3′ untranslated region. When poly(A) tails of the message prepared from eggs and oocytes were examined by RNase H digestion or reverse-transcription polymerase chain reaction, those of eggs were about 150 nucleotides longer than those of oocytes. These results suggest that translation of the message is stimulated during the oocyte maturation as a result of enhanced polyadenylation at its 3′-end. Finally a finding is presented that progesterone was converted to 11β-hydrexyprogesterone by the frog P450(11β), implying that the enzyme expressed in eggs may control a level of progesterone which is needed to initiate the oocyte maturation. [ABSTRACT FROM AUTHOR]

The solution structure of the major form of the reduced soluble fragment of rat microsomal cytochrome b5 has been solved through ¹H-NMR spectroscopy. The protein contains 98 amino acids. Proton assignment was available for residues 1-94, except 90 [Guiles, R. D., Basus, V. J., Kuntz., I. D. & Waskell, L. (19921 Biochemistry 31, 11 365-11 375] and has been confirmed. From 1722 NOEs, of which 1203 were found to be meaningful, a family of 40 energy-minimized structures has been obtained with average backbone rmsd (for residues 5–89) of 0.078±0.018nm and average target function of 0.0045 rim"+ no distance violations being larger than 0.029 rim. The structure has been compared with the X-ray structure of the oxidized rat mitochondrial isoenzyme and with that of the highly similar bovine microsomal isoenzyme in the oxidized form. The analysis of the elements of secondary structure is instructive in terms of their stability and of their occurrence in related structures, and of the capability of NMR and X-ray spectroscopy to observe them. Some detailed structural variations are noticed among the solved structures of the various isoenzymes and between solid and solution. The structural features in solution of the residues proposed to be involved in protein-protein recognition are found to be largely conserved with respect to the solid state. [ABSTRACT FROM AUTHOR]

The variability of Kluyveromyces lactis strains in sensitivity to glucose is correlated with genetic differences in Kluyveromyces hexose transporter (KHT) genes. The glucose sensitive strain J A6 was shown to contain an additional gene. KHT2, not found in strains that are less sensitive. KHT2 is tandemly arranged with KHT1 which is identical to the low-affinity transporter gene RAG1, except for the C-terminus. Sequence analysis indicated that most of KHT2 had been lost by a recombination event between KHT1 and KHT2 generating the chimeric gene RAG1. Recombination between KHT1 and KHT2 was also found in mutants of JA6 selected as 2-deoxyglucose resistant colonies. These mutants, like kht1 kht2 double mutants were unable to grow on glucose when respiration was blocked (Rag¯ phenotype) and glucose repression was strongly reduced, khtl or kht2 single mutants of JA6 were Rag' but still an influence of the kht mutations on glucose repression was detectable. Repression was not affected in a Rag mutant deleted for the phosphoglucose isomerase gene suggesting that the influence of transporter genes on repression is not caused by a reduction of the glycolytic flux. The data rather suggest that sensitivity to glucose repression is dependent on the rate of glucose uptake. [ABSTRACT FROM AUTHOR]

Some receptor tyrosine kinases such as the receptors for epidermal-growth factor (EGF) and plateletderived growth factor undergo polyubiquitination as a consequence of ligand binding. The EGF receptor is also ubiquitinated by treatment with herbimycin A, an ansamycin antibiotic widely used as a tyrosine kinase inhibitor. To investigate the mechanism of the receptor ubiquitination, we have established an assay system in which herbimycin-A-induced ubiquitination processes can be analyzed in vitro. We now show that herbimycin A treatment of the purified EGF receptor induces polyubiquitination of the receptor in rabbit-reticulocyte lysate. Both DEAE unadsorbed material (fraction I) and high salt eluate (fraction II) of the reticulocyte lysate are involved cooperatively in the ubiquitination process, where the ubiquitinconjugating enzyme UBC4 can functionally substitute for fraction I. A ubiquitin-protein ligase-like activity, partially purified from fraction II by DEAE anion-exchange chromatography, also functions in concert with UBC4. The precise mechanism of herbimycin A-induced ubiquitination of the EGF receptor is not fully understood, however, our present findings suggest that direct interaction with herbimycin A results in some modification of the receptor which is recognized by the ubiquitin-conjugating system in rabbitreticulocyte lysate. [ABSTRACT FROM AUTHOR]

Reports on signaling by interferon alpha, an extracellular factor that mediates a number of anti-viral and growth-suppressive effects, which requires two members of the Janus family of tyrosine kinases, Jak1 and Tyk2. Use of kinase-deficient mutants of both enzymes; Action of kinase-deficient versions of JAK can act as a dominant-negative fashion to suppress IFNalpha signaling; Effects of the overexpressed mutant kinases on the phosphorylation of the kinases themselves are unequal.

Reports on the characterization of cytochrome P-450 2E1 (CYP2E1) by a rapid turnover in the liver and some cell lines and the ability of substrates and heme iron ligands to inhibit enzyme degradation. Partial reversal of the effect of serum withdrawal by the addition of albumin to the culture medium; Slowing down of CYP2E1 degradation by the lysosomotropic agent ammonium chloride and the inhibitor of autophagocytosis 3-methyladenine.

Two distinct regions of plastocyanin, one hydrophobic and one acidic, are generally thought to be involved in the electron-transfer reactions with its physiological partners, cytochrome ƒ and photosystem 1. To probe the importance of the hydrophobic patch in the reaction with photosystem 1, seven mutant plastocyanin proteins have been constructed with the following mutations: Gly7Ala, Gly8Asp, Ser1 1 Asp, Ser1 1Gly, Pro36Gly, Ser85Thr and Gln88Asn. The electron-transler reaction was investigated by transient flash-photolysis absorption spectroscopy. All proteins remained active in photosystem 1 reduction, showing a biphasic reaction. However, the substitution in position 36 resulted in a drastic decrease in efficiency, suggesting that this residue is involved in a specific contact with photosystem 1. Measurements over a wide range of plastocyanin concentration, ionic strength and pH, showed different properties for the two kinetic phases. A mechanism involving a rate-limiting conformational change accounts well for the observations. Electron transfer from phastocyanin to photosystem 1 would thus require a conversion from an inactive to an active conformation of the complex. Both hydrophobic and electrostatic interactions are important in the dynamics. The structural integrity of a few critical residues, including Pro36, is essential for efficient photosystem 1 reduction. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) has been known for a Mug while to act as an inactivator of the soybean lipoxygenase-1 and cyclooxygenase. More recently. NO was shown to interact also with a mammalian 15-lipoxygenase [Wiesner. R., Rathmann, J., Holzhütter, H. G., Stöβer, R., Mäder. K., Nolting, H. & Kühn, H. (1996) Nitric oxide oxidises ferrous mammalian lipoxygenases to a pre-activated ferric species, FEBS Lett. 389, 229–232]. In this paper we present a detailed kinetic analysis of the interaction of NO with the 15-lipoxygenase from reticulocytes. Time courses of hydroperoxide formation were monitored after an anaerobic incubation of the enzyme with varying concentrations of NO and liar varying length of the incubation period. Owing to the presence of O2 during the enzymatic reaction, the inhibitory effect of NO declines in a time-dependent manner since NO is converted into non-reactive NO2 This is manifested as a lag phase of the time course. The lag phase becomes more pronounced if the enzyme is incubated over a fixed period (15 s) with increasing concentrations of NO. In contrast, increasing the length of the incubation period at fixed concentrations of NO diminishes the duration of the lag phase. These experimental findings can be accounted for by a kinetic model which assumes (a) fast reversible binding of NO m the inactive ferrous Fe(II) form of the enzyme and (b) slow irreversible conversion of the Fe(II)-NO complex into an activated ferric form of the enzyme which is susceptible to peroxide activation. The rate constants for these two different kinetic modes of NO action were estimated by fitting the solutions of tile model equations to the experimental time courses. The dissociation constant of the Fe(II)-NO complex amounts to 2.5 μM. Computer simulations performed on the basis of the model indicate that the response of the lipoxygenase to increasing intracellular NO concentrations depend upon the available peroxide tone: at low peroxide concentration the enzyme is initially trapped in the inactive ferrous form and thus may be activated by NO Via the activated ferric species. On the other hand, at high peroxide concentrations, a partial inhibition of the initially active enzyme is expected. [ABSTRACT FROM AUTHOR]

Protein SRP19 is a 144-amino-acid polypeptide that associates intimately with the signal-recognition particle RNA (SRP RNA) and serves as an important structural and functional component of the SRP. We investigated the structure and RNA-binding activity of the human SRP19 protein by the use of comparative sequence analysis, high-stringency structure prediction, proteolytic susceptibility, and site-directed mutagenesis. SRP19 was found to consist of two distinct regions (called N-terminal and C-terminal regions) that am separated by a boundary of approximately 12–15 amino acid residues. Both regions contain an a-helix and several β-strands that are connected by loops or turns. In agreement with the hypothetical model proteolytic susceptibility demonstrated the predominant accessibility of two sites: one in a surface loop of the N-terminal region (YLNNKKTIAEGR33), and another Site in the C-terminal tail at residues L129 and E133. The RNA-binding activities of mutant polypeptides with changes of conserved lysines and arginines (mutants K27Q, R33Q and R34Q) demonstrated that the proteolytically accessible loop of the N-terminal region is in direct contact with the SRP RNA. In contrast, alteration of a certain basic amino acid residues in the C-terminal region (R83, K116 and R118), as well as a deletion of four amino acid residues located at the boundary between the two regions, had no effect on the RNA-binding ability. The structural model that emerges from our data is thematically similar to that of ribosomal protein S5, the N-domain of which contains a loop motif believed to interact with double-stranded RNA. The presence of a similar structural feature in protein SRP19 has significant implications for the structure and function of the SRP19-RNA complex. [ABSTRACT FROM AUTHOR]

The gene that encodes for triosephosphate isomerase from Trypanosoma cruzi was cloned and sequenced. In T. cruzi, there is only one gene for triosephosphate isomerase. The enzyme has an identity of 72% and 68% with triosephosphate isomerase from Trypanosoma brucei and Leishmania mexicana, respectively. The active site residues are conserved: out of the 32 residues that conform the interface of dimeric triosephosphate isomerase from T. brucei, 29 are conserved in the T. cruzi enzyme. The enzyme was expressed in Escherichia coli and purified to homogeneity. Data from electrophoretic analysis under denaturing techniques and filtration techniques showed that triosephosphate isomerase from T. cruzi is a homodimer. Some of its structural and kinetic features were determined and compared to those of the purified enzymes from T. brucei and L. mexicana. Its circular dichroism spectrum was almost identical to that of triosephosphate isomerase from T. brucei. Its kinetic properties and pH optima were similar to those of T. brucei and L. mexicana, although the latter exhibited a higher Vmax with glyceraldehyde 3-phosphate as substrate. The sensitivity of the three enzymes to the sulfhydryl reagent methylmethane thiosulfonate (MeSO2-SMe) was determined; the sensitivity of the T. cruzi enzyme was about 40 times and 200 times higher than that of the enzymes from T. brucei and L. mexicana, respectively. Triosephosphate isomerase from T. cruzi and L. mexicana have the three cysteine residues that exist in the T. brucei enzyme (positions 14, 39, 126, using the numbering of the T. brucei enzyme); however, they also have an additional residue (position 117). These data suggest that regardless of the high identity of the three trypanosomatid enzymes, there are structural differences in the disposition of their cysteine residues that account for their different sensitivity to the sulthydryl reagent. The disposition of the cysteine in triosephosphate isomerase from T. cruzi appears to make it unique for inhibition by modification of its cysteine. [ABSTRACT FROM AUTHOR]

The dominating functional property of pulmonary surfactant is to reduce the surface tension at the alveolar air/liquid interface, and thereby prevent the lungs from collapsing at the end of expiration. In addition, the system exhibits host-defense properties. Insufficient amounts of pulmonary surfactant in premature infants causes respiratory distress syndrome, a serious threat which nowadays can be effectively treated by airway instillation of surfactant preparations. Surfactant is a mixture of many molecular species, mainly phospholipids and specific proteins, surfactant protein A (SP-A), SP-B, SP-C and SP-D. SP-A and SP-D are water-soluble and belong to the collectins, a family of large multimeric proteins which structurally exhibit collagenous/lectin hybrid properties and functionally are Ca2+-dependent carbohydrate binding proteins involved in innate host-defence functions. SP-A and SP-D also bind lipids and SP-A is involved in organization of alveolar surfactant phospholipids. SP-B belongs to another family of proteins, which includes also lipid-interacting polypeptides with antibacterial and lytic properties. SP-B is a 17.4-kDa homodimer and each subunit contains three intrachain disulphides and has been proposed to contain four amphipathic helices oriented pairwise in an antiparallel fashion. SP-A, SP-B and SP-D all have been detected also in the gastrointestinal tract. SP-C, in contrast, appears to be a unique protein with extreme structural and stability properties and to exist exclusively in the lungs. SP-C is a lipopeptide containing covalently linked palmitoyl chains and is folded into a 3.7-nm α-helix with a central 2.3-nm all-aliphatic part, making it perfectly suited to interact in a transmembranous way with a fluid bilayer composed of dipalmitoylglycerophosphocholine, the main component of surfactant. Homozygous genetic deficiency of proSP-B causes lethal respiratory distress soon after birth and is associated with aberrant processing of the precursor of SP-C. This review focuses on the chemical composition, structures and interactions of the pulmonary surfactant, in particular the associated proteins. [ABSTRACT FROM AUTHOR]

Ribonuclease P (RNase P) from wheat nuclei has been purified over 1000-fold, using wheat germ extract as starting material and a combination of poly(ethytenglycol) precipitation and column chromatograpliy. The enzyme was shown to be of nuclear origin by its characteristic ionic requirements: for optimum activity it requires 0.5-1.5 mM Mg2+, which can be partly replaced by Mn2+. With about 100 kDa, wheat nuclear RNase P has the lowest molecular mass reported so far for a eukaryotic RNase P. The enzyme has an isoelectric point of 5.0 and a buoyant density of 1.34 g/ml in CsCl, suggesting the presence of a nucleic acid component: it is, however, insensitive against treatment with micrococcal nuclease. Wheat germ RNase P requires an intact tertiary structure of the pre-tRNA substrate; its cleavage efficiency is also influenced by the presence of an intron, and by the nature of the 3' terminus of the substrate. The apparent Km and Vmax, for an intronless plant pre-tRNATyr are 10.3 nM and 1.12 fmol/min, respectively. [ABSTRACT FROM AUTHOR]

In the first part of this work [Heinrich, R., Montero, F., Klipp, E., Waddell, T. G. & Meléndez-Hevia, E. (1997) Eur. J. Biochem. 243, 191 -201]. the kinetic and thermodynamic constraints under which an optimal glycolysis must be designed have been analysed. In the second part, we present a chemical analysis of the glycolytic pathway in order to determine if its design is chemically optimized according the possibilities that a glycolytic design can have. Our results demonstrate that glycolysis in modern-day cells (from glucose to lactate) has an optimized design for maximizing the flux of ATP production, and a thermodynamic profile which guarantees a high kinetic efficiency. We also discuss some cases of paleometabolism for this pathway as alternative metabolic pathways, less optimized, that exist in some bacteria. Our analysis relates mainly to metabolism designed under constant chemical affinity (substrates and products of the pathway constant), where the target of optimization can be the flux of ATP production. We also discuss the case of an externally imposed input flux, whose target of optimization is the stoichiometric yield of ATP. [ABSTRACT FROM AUTHOR]

NMR signals for HisB5 NδH and HisEF5 NεH protons of sperm whale and horse apomyoglobins were assigned and compared with the corresponding signals of the holoproteins in tertns of pH and temperature dependence behaviors of their shifts and line widths in order to gain insight into structural difference between the apoproteins and the holoproteins. Since these protons are involved in internal hydrogen bonds at the interfaces between the B helix and the GH corner and between the EF corner and the H helix, local structures of the interfaces in these proteins have been inferred from the analyses of these signals. A large difference in the line width of HisEF5 NεH proton signal between the apoproteins and the holoproteins strongly suggested that a sizable structural alteration is induced in the EF-H interface by the removal of heine. However, the results for HisB5 NδH proton resonance indicated the absence of a significant structural alteration in the B-GH inter[ace by heine extraction. These results are consistent with the data obtained from mutation [Hughson, F. M. & Baldwin, R. L. (1989) Biochemitry, 28. 44154422] and amide-proton-exchange kinetic [Hughson, F. M., Wright., E E. & Baldwin, R. L. (1990) Science 249, 1544-15481 studies, which indicated that the A, B, G and H helices in apomyoglobin maintain the same packing as they do in holoprotein. [ABSTRACT FROM AUTHOR]

Amino-terminal and carboxy-terminal deletion mutagenesis have been used to identify structurally and functionally critical regions of recombinant wild-type human phenylalanine hydroxylase (wt-hPAH; Ser2-Lys452). The wild-type form consisted of dimeric and tetrametic forms in equilibrium, and only the isolated tetrameric form showed positive cooperativity of substrate (L-Phe) binding (Hill coefficient h = 2.2, S0.5=154 µM) The deletion mutants lacking the carboxy-terminal 24 amino acids hPA H(Ser2 Gln428) and hPAH(Gly103-Gln428) formed catalyticallyiy active dimers, and incubation with L-Phe did not promote the formation of tetramers, a characteristic property of dimeric wt-hPAH. The carboxy terminus thus seems to contain a motif required for dimer-dimer interaction in wt- hPAH. The deletion mutants hPAH(Asp112- Lys452), hPAH(Ser2-Gln428) and hPAH (Gly103-GLn428) were all activated by prior incubation with L-Phe,. but did not reveal any positive cooperativity of substrate binding (h = 1.0). The activation by L-Phe was accompanied by a measurable conformational change (as probed by intrinsic fluorescense spectroscopy) only in the enzyme forms containing the amino-terminal sequence, i.e, wt-hPAH and the Ser2-Gln428 mutant. The amino-terminal deletion mutant hPAH(Asp112) Lys452) and hPAH(Gly103-Gln428) revealed high specific activity, increased apparent affinity lot LPhe (S0.3 =60 µM ) and a tryptophan fluorescence emission spectrum similar to that of the L-Phe-activated wt-hPAH. Moreover, prior incubation of the enzymen forms with lysophosphalidylcholine, a commonly used activator of the PAH, only increased the activity of those forms containing the wt-hPAH aminoterminal sequence. Our results are comparable with a model in which incubation of wt-hPAH with L-Phe induces both a conformational change (with cooperativity in the tetrameric enzyme) which releives the inhibition imposed by the amino-terminal domain to the high-affinity binding of L-Phe, and an additional activation, as observed for the truncated forms lacking the amino-terminal. [ABSTRACT FROM AUTHOR]

Myosin-associated giant protein kinases of the titin/twitchin-like superfamily have previously been implicated in the regulation of muscle function, based on genetic and physiological studies. We find that recombinant, constitutively active Caenorhabditis elegans and Aplysia twitchin kinase fragments differ in their catalytic activities and peptide-substrate specificifies, as well as in their sensitivities to the naphthaIene sulfonamide inhibitors 1-(5-chloronaphthalenesulfonyl)-1H-hexahydro-l,4-diazepine (ML-7) and 1-(5-iodonaphthalenesulfonyl)-1H-hexahydro-1,4-diazepine (ML-9). The constitutively active Aplysia' twitchin kinase fragment has a remarkably high activity (Vmax > 100 µmol · min-1 · mg-1) towards some substrate peptides. The autoinhibited forms of these twitchin kinases can be activated in a Ca2+-dependent rammer by the dimeric form of the S100A1 protein (S100AI2). The twitchin kinase S100Al2-binding site can also bind Ca2+/calmodulin but neither kinase is activated by calmodulin. The data provide a functional basis for the ongoing crystallographic study of twitchin kinase fragments. [ABSTRACT FROM AUTHOR]

Human apolipoprotein A-II (apo A-II)consists of throe potential amphipathic helices of 17 residues each, which contribute to the lipid-binding properties of ibis apolipoprotein. The conformation and lipidbinding properties of these peptides either as single-helix or as two-helix peptides, were investigated by turbidity, fluorescence, electron-microscopy and circular-dichroism measurements, and arc compared in this article. The lipid affinity of shorter C-terminal segments of apo A-II was compared with those of the single-helix or two-helix peptides to define the minimal peptide length required for stable complex formation The properties of the apo-A-II-(l3-48)-peptide were further compared with those of the same segment after deletion of the Ser31 and Pro32 residues, because the deleted apo-A-II-(l3-30)-(33-48)peptide, is predicted to form a long uninterrupted helix. The single helices of apo A-II could not form stable complexes with phospholipids, and the helix 13 48 was mi active either. The apo-A-II-(37-77)-peptide and turn-he:l ix segment spanning residues - the apo-A-II-(40-73)-peptide could form complexes with lipids, which appear as discoidal particles by negative staining electron microscopy. The shortest C-terminal domain of apo A-II able to associate with lipids to form stable complexes was the apo-A-II-(40-773)-peptide, which consisted of the C-terminal helix, a β-turn and wart of the preceding helix. The shorter apo-A-II-(49-77)-peptide, and the helical apo A-II-(-30)-(33-48)-peptide, could also associate with phospholipids. The complexes formed were, however; less stable, as they dissociated outside the transition temperature range of the phospholipid. These data suggest that the C-terminal pair of helices of apo A-II, which is the most hydrophobic pair, is responsible for the lipid-binding properties of the entire protein. The N-terminal pair of helices of apo A-II at residues 13-48 does not associate tightly with lipids. The degree of internal similarity and the cooperativity between the helical segments of apo A-II is thus less pronounced than in apo A-I or apo A-IV. The N-terminal and C-terminal domains of apo A-II appear to behave as two distinct entities with regard to lipid-protein association. [ABSTRACT FROM AUTHOR]

We have labelled a DNA-binding site on the globular domain of histone H5 (GH5) by ultraviolet activated cross-linking of a self:complementary 5-bromodeoxyuridine (SBrU)-substituted oligonucleotide with the sequence 5'-AGCGA5BrUATCGCT-3'. Cross-linking was to His62, mainly to the protein backbone. This observation provides further support for the mode of binding of GH5 to DNA proposed on the basis of the similarity between the X-ray crystal structure of GH5 and the DNA-bound structures of catabolite activator protein and hepatic nuclear factor 3γ [Ramakrishnan, V. (1994) Curr. Opin. Struct. Biol. 4, 44 - 50]. [ABSTRACT FROM AUTHOR]

Describes the functional characteristics of a variant thyrotropin receptor. Thyrotropin responsiveness of the receptor; Transient expression of the wild types; Display of constitutive activity; Affinity for the bovine thyrotropin.

Examines the presence of acetylcholinesterase in dendrobaena veneta with forms sensitive and insensitive to phosphatidylinositol phosphalipase C. Enzyme analysis through gel-filtration chromatography, sedimentation analysis and polyacrylamide gel electrophoresis; Substrate specificity; Inhibition of acetylcholinesterase.

Examines the developmental expression of CYP2E1 protein in the human liver following birth independently of the gestational age. Role of the cytochrome P-450 in the biotransformation of drugs and other hydrophobic molecules by liver; Nucleic acid content during the period; Methylation status of CpG residues.

Examines the synthesis and differential properties of creatine analogues as inhibitors for human creatine kinase enzymes. Consideration for the apolar aromatic moiety of compounds; Inhibitory activity of the tested compounds; Manifestation of isoenzyme selectivity.

Discusses the purification of Escherichia coli pro-haemolysin, comparing its properties with that of the mature alpha-haemolysin. Aggregate formation in aqueous media; Direct measurement of protein binding to liposomal membranes; Intrinsic fluorescence emission of the protein upon layer binding.

Examines the trans-acting factors, detoxication enzymes and hepatitis B virus replication in a set of human hepatoma cell lines. Isolation of hepatoma cell lines from a single tumor; Albumin expression in cells; Gene encoding transcription factor activities.

Examines the structure of the human gene encoding of the phosphorylase kinase beta subunit. Primary structure of the amino acid sequence identity; Homology and splicing of exons; Screening of the chromosome 16-specific genomic library.

Focuses on the successive amino-terminal proteolysis of the large subunit of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) by vacuolar enzymes from French bean leaves. Lack of significant degradation products of the subunit; Incubation of rubisco with vacuolar lysates prepared from the senescing primary leaves; Determination of amino terminal amino acid sequences.

Examines how DNA is replicated with high fidelity and how defects in these processes can lead to a higher than normal mutation rate in cancer cells. Key steps and principles for high fidelity replication; Observation of mutator phenotype in tumor cells; Germ line mutation in genes.

We have designed an assay to measure the rate of initiation of DNA synthesis in Friend erythroleukemia cells and have shown that this parameter is reduced by γ-radiation and treatment with 4'-demethyl-epipodophyllotoxin-9-(4.6-O-ethylene-β-D-glucopyranoside) (VP-16). It is concluded, that double-strand breaks in DNA are the immediate cause for this effect. The decrease in the rate of replicon initiation is affected differently by different agents such as cis-diamminedichloroplatinum(II), cycloheximide, staurosporine, and 3-aminobenzamide. The analysis of these results indicates that the observed parial decrease of the rate of DNA initiation is most probably transmitted from the site of damage to the initiation site by one or more phosphorylation/dephosphorylation steps. It does not require de navo synthesis of protein factors, but is probably dependent on poly(ADP-ribosyl)ation of chromatin at the site of DNA breaks. [ABSTRACT FROM AUTHOR]

The frameshift protein p6* encoded directly upstream of the protease in the human immunodeficiency virus type 1 (HIV-1) pol reading frame is thought to be a natural inhibitor of protease activation and to play a role in the polyprotein processing of Gag and Gag-pol precursors. To allow structural characterization of the p6* coding region was cloned into the vector pGEX-KG and expressed in Escherichia coli as a fusion protein with glutathione S-transferase (GST) under the control of the tac promoter. Thrombin cleavage of the construct resulted in a 70-amino-acid polypeptide which is extended by two additional residues at the N-terminus compared to the natural p6* sequence. The native purification procedure including an affinity and a size-exclusion chromatography step yielded sufficient amounts of highly pure protein suitable for NMR spectroscopy. Fluorescence. circular dichroism and 'H-NMR spectroscopy were applied to characterized the structure of the protein. Two-dimensional NMR spectra provided essentially complete sequence-specified resonance assignments at pH 5.9. Although there is evidence for a helix-forming tendency in the N-terminus of the protein, the experiments indicate that p6* has no overall stable secondary or tertiary structure with the single tryptophan exposed in aqueous solution. However, the results reported herein open the way to characterize further the interaction of p6* with the HIV-1 protease in structural and functional in vitrostudies. [ABSTRACT FROM AUTHOR]

Similar to previous observations in rabbit muscle, chronic low-frequency stimulation suppressed parvalbumin expression in fast-twitch muscles of the rat. In extensor digitorum longus and tibialis anterior muscles, parvalbumin mRNA levels steeply declined with apparent half-lives of approximately 26 h and 45 h, respectively. Measurements of parvalbumin synthesis indicated that the reduction in mRNA was immediately transmitted to the level of translation. Relative parvalbumin synthesis rates decayed with an apparent half-life of approximately 60 h. Both the decrease in parvalbumin mRNA and synthesis considerably preceded the decay of parvalbumin protein. Although parvalbumin synthesis had approached zero in 14-day-stimulated muscles, parvalbumin content started to decrease only after some delay (28-day-stimulated muscles still contained 40-50% of their normal parvalbumin content). The lag time between fully suppressed synthesis and the onset of parvalbumin decay, as well as the stability of parvalbumin against tryptic cleavage in the presence of Ca2+ and Mg2+, indicated proteolysis as an important post-translational control of parvalbumin levels. The decrease in parvalbumin mRNA followed a similar time course as that of the mRNA specific to the fast myosin heavy chain HCIIb. After complete suppression. parvalbumin mRNA reached control levels 4 days after cessation of stimulation, which demonstrates the complete reversibility of the stimulation-induced parvalbumin suppression. These results show that a slow motoneuron-like impulse pattern rapidly silences the parvalbumin gene. thus overriding fast-fiber-type-specific programs of gene expression. Due to post-transcriptional regulation and the stability of parvalbumin, this high responsiveness of adult skeletal muscle to altered neuromuscular activity is more conspicuous at the mRNA level than at the protein level. [ABSTRACT FROM AUTHOR]

In this work we present the characterization of a hemidiscoidal phycobilizome type of the heterocyst-formng cyanobacterium Anabaena sp PCC 7120. The phycobilisome of this organism contains alloopycocyanin, phycocyanin and phycoerythrocyanin, similar to the closely related thermophilic cyanobacterium Mastigocladus laminasus. Intact Phycobilisomes exhibit an absorption maximum at 619 nm and two fluorescence maxima at 664 nm and 680 nm, corroborating the presence of a complete energy pathway along the antenna. Upon dissociation, the phycobiliproteins were released from the phycobilisome. One phycoerythrocyanin, one phycocyanin and three allophycocyanin complexes were isolated by ion-exchange chromatography and characterized by absorption and fluorescence spectroscopy and by SDS /PAGE. The polypeptides contained in the phycobilisome of Anabaena sp. PCC 7120 were subjected to SDS/PAGE, blotted onto poly(vinylidendifluoride) membranes and identified by amino-terminal sequences analysis. The amino-terminal sequences of the polypeptides belonging to the phycoerythrocyanin and phycocyanin families were identical with the derived sequences of their corresponding genes. Partial amino-terminal sequences of the polypeptides belonging to the allophycocyanin family are presented here. Our results show that the phycobiliproteins and linker polypeptides from Anabaena sp. PCC 7120 are similar to the phycobilisome components characterized in other cyanobacteria. The phycobilisome of Anabaena sp. PCC 7120 was extensively analyzed by electron microscopy. It differs from the common hemidiscoidal tricylinderical, six-rod phycobilisome type by a core domain consisting of five core cylinders surrounded by up to eight rods radiating in a hemidiscoidal manner. One rod is linked to each basal core cylinder, whereas the remaining core cylinders bind two rods each. [ABSTRACT FROM AUTHOR]

It is becoming increasingly apparent that translational control plays an important role in the regulation of gene expression in eukaryotic cells. Most of the known physiological effects on translation are exerted at the level of polypeptide chain initiation. Research on initiation of translation over the past five years has yielded much new information, which can be divided into three main areas: (a) structure and function of initiation factors (including identification by sequencing studies of consensus domains and motifs) and investigation of protein-protein and protein-RNA interactions during initiation: (b) physiological regulation of initiation factor activities and (c) identification of features in the 5' and 3' untranslated regions of messenger RNA molecules that regulate the selection of these mRNAs for translation. This review aims to assess recent progress in these three areas and to explore their interrelationships. [ABSTRACT FROM AUTHOR]

Metabolic defects in phytanic acid catabolism have been shown to be connected with a number of human diseases which can lead to lethal defects of the nervous system and other organs. These effects are probably a result of the very high accumulation of phytanic acid in tissues throughout the body, due to defects in phytanic acid oxidation, the peroxisome being a major site for this process. The nuclear hormone receptors peroxisome proliferator-activated receptor and retinoid X receptor (RXR) have been shown to function as transcription factors in the control of the peroxisomal enzyme expression. Known activators of peroxisome proliferator-activated receptor include polyunsaturated fatty acids and, for RXR, the 9-cis isomer of retinoic acid. Here we report that phytanic acid is also a natural ligahd for RXRa, being able to activate a RXR-responsive promoter. We present evidence that phytanic acid binds to RXRa, promotes formation of an RXRa/RXR response element complex (as detected by gel retardation), and induces a RXRa conformational change similar to that induced by 9-cis-retinoic acid (as detected by protease sensitivity). These results suggest an involvment of RXRa in the control of fatty acid metabolism and could simply that RXRs have a role in the disease effects resulting from defective phytanic acid catabolism. [ABSTRACT FROM AUTHOR]

The interaction between photosystem I (PS I) and flavodoxin from the cyanobacterium Synechococcus sp. PCC 7002 was investigated by covalent cross-linking in the presence of a hydrophilic cross-linker, Nethyl-3-(3-diaminopropylicarbodiimide. Under the experimental conditions employed, five distinct crosslinking products of flavodoxin and PS I subunits are formed. Immunoblot analyses show that these species are the result of cross-linking of flavodoxin to PsaC, PsaD, an unidentified low-molecular-mass PS I polypeptide, and a 15-kDa subunit. The latter has been indirectly identified us tile PsaF subunit. Analysis of the interaction of flavodoxin with PS I from a psaE mutant indicates that the PsaF subunit is required for correct complex formation between flavodoxin and PS I, although this subunit is not directly crosslinked to flavodoxin. In addition, the cross-linking products of PsaD with PsaC and PsaL, and PsaE with PsaF are observed. The covalent complex of flavodoxin and PS I is shown to be fully inhibited with respect to electron transfer to soluble flavodoxin, ferredoxin or ferredoxin:NADP oxidoreductase. [ABSTRACT FROM AUTHOR]

In the presence of cyanide, populations of yeast cells can exhibit sustained oscillations in the concentration of glycolylic metabolites, NADH and ATP. This study attempts to answer the long-standing question of whether and how oscillations of individual cells are synchronized. It shows that mixing two cell populations that oscillate 180° out of phase only transiently abolishes the macroscopic oscillation. After a few minutes. NADH fluorescence of the mixed population resumes oscillations up to the original amplitude. At low cell densities, addition of acetaldehyde causes transient oscillations. At higher cell densities, where the oscillations are autonomous, 70 µM acetaldehyde causes phase shifts. Extracellular acetaldehyde is shown to oscillate around the 70 µm level. We conclude that acetaldehyde synchronizes the oscillations of the individual cells. [ABSTRACT FROM AUTHOR]

To investigate in a direct way the interaction between a precursor protein and phospholipids, monolayer studies were performed using the purified precursor of Escherichia coli outer-membrane protein PhoE. It was demonstrated that prePhoE can rosen efficiently into monolayers of dioleoyiglycerophosphoglycerol (Ole2GroPGro) and dioleoylglycerophosphoethanolamine (Ole2GroPEtn), this insertion was mainly driven by hydrophobic forces. Compared with previous results obtained with PhoE signal peptide, the full-length precursor protein does not show tire specific interaction with acidic lipids. PrePhoE inserted into a Ole2GroPGro occupies an area of 28 ± 30 nm²/molecule, which is approximately 10-fold larger than the area occupied by the PhoE signal peptide. The purified mature PhoE protein has a lower capacity to insert into Ole2GroPGro and Ole2GroPEtn monolayers and is, in contrast to prePhoE. fully accessible to proteinase K after interacting with a Ole2GroPGro monolayer. The results demonstrate that in the context of the precursor protein both the signal sequence and mature domain of prePhoE insert into lipid monolayers. It was found that PhoE, like prePhoE, can form in vitro a complex with the cytosolic chaperone SecB. Complexation with SecB increases the insertion of (pre)PhoE into acidic lipid monolayers. The high lipid affinity of prePhoE was also demonstrated by vesicle-binding experiments which showed that SecB dissociates from the SecB-prePhoE complex upon binding of the precursor to the bilayer. The implications of these findings for preprotein translocation are discussed and in addition some extrapolations to the insertion of PhoE into the outer membrane are made. [ABSTRACT FROM AUTHOR]

The first dimeric catalase-peroxidase of eucaryotic origin, an intracellular hydroperoxidase from Penicillium simplicissimum which exhibited both catalase and peroxidase activities, has been isolated. The enzyme has an apparent molecular mass of about 170 kDa and is composed Of two identical subunits. The purified protein has a pH optimum for catalase activity at 6.4 and for peroxidase at 5.4. Both activities are inhibited by cyamide and azide whereas 3-amino-1,2,4-triazole has no effect. 3,3'-Diaminobenzidine, 3,3',-dimethoxybenzidine, guaiacol, 2,6-dimethoxyphenol and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) all serve as substrates. The optical spectrum of the purified enzyme shows a Soret band at 407 nm. Reduction by dithionite results in the disappearance of the Soret band and formation of three absorption maxima at 440, 562 and 595 nm. The prosthetic group was identified as a protoheme IX and EPR spectroscopy revealed the presence of a histidine residue as proximal ligand. In addition to the catalase-peroxidase, an atypical catalase which is active over A broad pH range was also partially purified from P. simplicissimum. This catalase is located in the periplasm and contains a chlorine-type heme as prosthetic group. [ABSTRACT FROM AUTHOR]

Formylmethanofuran dehydrogenases are molybdenum or tungsten iron-sulfur proteins containing a pterin dinucleotide cofactor. We report here on the primary structures of the four subunits FwdABCD of the tungsten enzyme from Methanobacterium thermoautotrophicum which were determined by cloning and sequencing the encoding genes fwdABCD. FwdB was found to contain sequence motifs characteristic for molybdopterin-dinucleotide-containing enzymes indicating that this subunit harbors the active site. FwdA, FwdC and FwdD showed no significant sequence similarity to proteins in the data bases. Northern blot analysis revealed that the four fwd genes form a transcription unit together with three additional genes designated fwdE, fwdF and fwdG. A 17.8-kDa protein, both containing two [4Fe-4S] cluster binding motifs, were deduced from fwdE and fwdG. The open reading frame fwdF encodes a 38.6-kDa protein containing eight binding motifs [4Fe-4S] clusters suggesting the gene product to be a novel polyferredoxin. All seven fwd genes were expressed in Escherichia coli yielding proteins of the expected size. The fwd operon was found to be located in a region of the M. thermoautotrophicum genome encoding molybdenum enzymes and proteins involved in molybdopeterin biosynthesis. [ABSTRACT FROM AUTHOR]

Examines the affinity of human erythrocyte porphobilinogen synthase for Zn[sup 2+] and Pb[sup 2+]. Supplementation with metal-ion buffers to control free Zn[sup 2+] and Pb[sup 2+]; Use of a blood sample of the common 1-1 phenotype.

Presents a structure and expression analysis of the gdcsPA and gdcsPB genes encoding two P-isoproteins of the glycine-cleavage system from Flaveria pringlei. Subdivision of the P-protein genes into two parts based on the lengths of exons and intervening sequences; Presence regulatory elements acting with a distinct organ preference.

Treatment of bean cell walls with a pure endopolygalacturonase of the bean pathogen Colletotrichum lindemuthianum race β released oligogalacturonides and pectic fragments which were separated according to their charge and size. Among galacturonic-acid-containing components, elicitors and suppressors of the plant cell wall hydroxyproline-rich glycoprotein (HRGP) were recovered. Two active small oligogalacturonides with degrees of polymerization of 2 and 3 were characterized by high-performance anion-exchange-chromatography pulsed amperometric detection and fast-atom-bombardment mass spectrometry; they elicited 40-70% hydroxyproline increase within 48 hours at 450 nmol/bean cutting. In contrast, pectic fragments of higher molecular mass, predominantly composed of galacturonic acid and containing sugars typical of the rhamnogalacturonan II domain of pectic polysaccharides, had the ability to substantially suppress hydroxyproline deposition. Maximum suppressor activity, 30-40% below the activity of the control, occurred in 48 hours. In view of the low one-cycle turnover of these proteins in the cell wall and of their structural role, these changes might significantly affect cell wall properties. Elicitation and/or suppression of hydroxyproline were correlated to modifications of HRGP-extensin gene expression. Northern-blot analysis of RNA showed that changes in the transcript intensity became clearly visible within the first 12 hours after the start of either treatment. The results show that pectic components of the plant extracellular matrix have the potential to regulate wall matrix biogenesis. Implications of this finding in plant defense and development are discussed. [ABSTRACT FROM AUTHOR]