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A spontaneous mutant of Rhodobacter sphaeroides f. sp. denitrificans IL-106 was found to excrete a large amount of a red compound identified as coproporphyrin III, an intermediate in bacteriochlorophyll and heme synthesis. The mutant, named PORF, is able to grow under phototrophic conditions but has low levels of intracellular cysteine and glutathione and overexpresses the cysteine synthase CysK. The expression of molybdoenzymes such as dimethyl sulfoxide (DMSO) and nitrate reductases is also affected under certain growth conditions. Excretion of coproporphyrin and overexpression of CysK are not directly related but were both found to be consequences of a diminished synthesis of the key metabolite S-adenosylmethionine (SAM). The wild-type phenotype is restored when the gene metK encoding SAM synthetase is supplied in trans. The metK gene in the mutant strain has a mutation leading to a single amino acid change (H145Y) in the encoded protein. This point mutation is responsible for a 70% decrease in intracellular SAM content which probably affects the activities of numerous SAM-dependent enzymes such as coproporphyrinogen oxidase (HemN); uroporphyrinogen III methyltransferase (CobA), which is involved in siroheme synthesis; and molybdenum cofactor biosynthesis protein A (MoaA). We propose a model showing that the attenuation of the activities of SAM-dependent enzymes in the mutant could be responsible for the coproporphyrin excretion, the low cysteine and glutathione contents, and the decrease in DMSO and nitrate reductase activities. doi: 10.1128/JB.01342-09

We found that Escherichia coli tolC mutants showed increased sensitivity to 5-aminolevulinic acid (ALA), a precursor of porphyrins. The tolC mutant cells grown in the presence of ALA showed a reddish brown color under visible light and a strong red fluorescence under near-UV irradiation. Fluorescence spectrometry and high-performance liquid chromatography analysis showed that the tolC mutant cells grown in the presence of ALA accumulated a large amount of coproporphyrin(ogen) intracellularly. In contrast, the wild-type cells produced coproporphyrin extracellularly. The tolC mutant cells grown in the presence of ALA, which were capable of surviving in the dark, were killed by near-UV irradiation, suggesting that the intracellular coproporphyrin(ogen) renders these cells photosensitive. These results suggest that the TolC-dependent efflux system is involved in the exclusion of porphyrin(ogen)s in E. coli.

Porphyromonas gingivalis lipid A is heterogeneous with regard to the number, type, and placement of fatty acids. Analysis of lipid A by matrix-assisted laser desorption ionization-time of flight mass spectrometry reveals clusters of peaks differing by 14 mass units indicative of an altered distribution of the fatty acids generating different lipid A structures. To examine whether the transfer of hydroxy fatty acids with different chain lengths could account for the clustering of lipid A structures, P. gingivalis lpxA ([lpxA.sub.Pg]) and [lpxD.sub.Pg] were cloned and expressed in Escherichia coli strains in which the homologous gene was mutated. Lipid A from strains expressing either of the P. gingivalis transferases was found to contain 16-carbon hydroxy fatty acids in addition to the normal E. coli 14-carbon hydroxy fatty acids, demonstrating that these acyltransferases display a relaxed acyl chain length specificity. Both LpxA and LpxD, from either E. coli or P. gingivalis, were also able to incorporate odd-chain fatty acids into lipid A when grown in the presence of 1% propionic acid. This indicates that E. coli lipid A acyltransferases do not have an absolute specificity for 14-carbon hydroxy fatty acids but can transfer fatty acids differing by one carbon unit if the fatty acid substrates are available. We conclude that the relaxed specificity of the P. gingivalis lipid A acyltransferases and the substrate availability account for the lipid A structural clusters that differ by 14 mass units observed in P. gingivalis lipopolysaccharide preparations.

High-valent iron species are powerful oxidizing agents in chemical and biological catalysis. The best characterized form of an Fe(V) equivalent described in biological systems is the combination of a b-type heme with Fe(IV)=O and a porphyrin or amino acid cation radical (termed Compound I). This work describes an alternative natural mechanism to store two oxidizing equivalents above the ferric state for biological oxidation reactions. MauG is an enzyme that utilizes two covalently bound c-type hemes to catalyze the biosynthesis of the protein-derived cofactor tryptophan tryptophylquinone. Its natural substrate is a monohydroxylated tryptophan residue present in a 119-kDa precursor protein. An EPR-silent di-heme reaction intermediate of MauG was trapped. Mossbauer spectroscopy revealed the presence of two distinct Fe(IV) species. One is consistent with an Fe(IV)=O (ferryl) species ([delta] = 0.06 mm/s, [DELTA][E.sub.Q] = 1.70 mm/s). The other is assigned to an Fe(IV) heme species with two axial ligands from protein ([delta] = 0.17 mm/s, [DELTA]EQ = 2.54 mm/s), which has never before been described in nature. This bis-Fe(IV) intermediate is remarkably stable but readily reacts with its native substrate. These findings broaden our views of how proteins can stabilize a highly reactive oxidizing species and the scope of enzyme-catalyzed posttranslational modifications. ferryl | posttranslational modification | spectroscopy tryptophan tryptophylquinone (TTQ) | free radical

An efficient synthesis of porphobilinogen by employing Mukaiyama aldol reaction between the regioselectively formed silyl enol ether and the acetal of methyl 5-azidolevulinate is reported.

The cytoplasmic membrane protein CcmC is, together with other Ccm proteins, a component for the maturation of c-type cytochromes in Gram-negative bacteria. A Pseudomonas fluorescens ATCC 17400 ccmC mutant is cytochrome c-deficient and shows considerably reduced production of the two siderophores pyoverdine and quinolobactin, paralleled by a general inability to utilize various iron sources, with the exception of haem. The ccmC mutant accumulates in a 5-aminolevulinic acid-dependent synthesis a reddish, fluorescent pigment identified as protoporphyrin IX. As a consequence a visA phenotype similar to that of a ferrochelatase-deficient hemH mutant characterized by drastically reduced growth upon light exposure was observed for the ccmC mutant. The defect of iron-protoporphyrin formation was further demonstrated by the failure of ccmC cell-free proteinase K-treated extracts to stimulate the growth of a haem auxotrophic hemH indicator strain, compared to similarly prepared wild-type extracts. In addition, the ccmC mutant did not sustain hemH growth in cross-feeding experiments while the wild-type did. Significantly reduced resistance to oxidative stress mediated by haem-containing catalases was observed for the ccmC mutant. A double hemH ccmC mutant could not be obtained in the presence of external haem without the hemH gene in trans, indicating that the combination of the two mutations is lethal. It was concluded that CcmC, apart from its known function in cytochrome c biogenesis, plays a role in haem biosynthesis. A function in the regulatory co-ordination of iron acquisition via siderophores, iron insertion into porphyrin via ferrochelatase and iron--protoporphyrin export for cytochrome c formation is predicted.

The haem pigment of Porphyromonas gingivalis is composed of [micro]-oxo bishaem, [[Fe(III)PPIX].sub.2]O, but the nature of that generated by Prevotella species has not been established. Mossbauer, Raman and UV-visible spectrophotometry were used to characterize the haem pigment of Prevotella intermedia and Prevotella nigrescens. M6ssbauer and Raman spectroscopy revealed the major haem species to be monomeric iron protoporphyrin IX, Fe(III)PPIX.OH (haematin). The terminal growth pH of both species on blood agar was between 5.8 and 6.0, which favours the formation and maintenance of monomeric Fe(III)PPIX.OH. Incubation of Pr. nigrescens and Pr. intermedia with oxyhaemoglobin at pH 6.5 resulted in formation of aquomethaemoglobin which was degraded to generate Fe(III) PPIX.OH which in turn became cell-associated, whilst incubation at pH 7*5 resulted in formation of [[Fe(III)PPIX].sub.2]O. It is concluded that both Prevotella species degrade oxyhaemoglobin to form [[Fe(III)PPIX].sub.2]O as an intermediate, which is converted to Fe(III)PPIX.OH through a depression in pH. The low pH encourages cell-surface deposition of insoluble Fe(III)PPIX.OH which would act as a barrier against oxygen and reactive oxygen species, and also protect against [H.sub.2][O.sub.2] through its inherent catalase activity.

The facultative photosynthetic bacterium Rhodobacter capsulatus can adapt from an anaerobic photosynthetic mode of growth to aerobic heterotrophic metabolism. As this adaptation occurs, the cells must rapidly halt bacteriochlorophyll synthesis to prevent phototoxic tetrapyrroles from accumulating, while still allowing heme synthesis to continue. A likely control point is Mg chelatase, the enzyme that diverts protoporphyrin IX from heme biosynthesis toward the bacteriochlorophyll biosynthetic pathway by inserting [Mg.sup.2+] to form Mg-protoporphyrin IX. Mg chelatase is composed of three subunits that are encoded by the bchI, bchD, and bchH genes in R. capsulatus. We report that BchH is the rate-limiting component of Mg chelatase activity in cell extracts. BchH binds protoporphyrin IX, and BchH that has been expressed and purified from Escherichia coli is red in color due to the bound protoporphyrin IX. Recombinant BchH is rapidly inactivated by light in the presence of [O.sub.2], and the inactivation results in the formation of a covalent adduct between the protein and the bound protoporphyrin IX. When photosynthetically growing R. capsulatus cells are transferred to aerobic conditions, Mg chelatase is rapidly inactivated, and BchH is the component that is most rapidly inactivated in vivo when cells are exposed to aerobic conditions. The light- and [O.sub.2]-stimulated inactivation of BchH could account for the rapid inactivation of Mg chelatase in vivo and provide a mechanism for inhibiting the synthesis of bacteriochlorophyll during adaptation of photosynthetically grown cells to aerobic conditions while still allowing heme synthesis to occur for aerobic respiration.

Research has been conducted on Enterococus faecalis strain V583. The identification of chromosomal gene which encodes heme-containing cytoplasmic catalase in this strain has been carried out, and the details are reported.

Research has been conducted on the carbaporphyrins. The reaction of these compounds with silver(I) acetate in methanol-CH (sub)2 Cl (sub)2 has produced silver(III) complexes and the details are reported.

Research has been conducted on the putative cytotoxin, peroxynitrile. Results indicate that this compound can be decomposed catalytically by water-soluble Fe(III) porphyrin complexes.

Research has been conducted on the light-harvesting arrays with perylene-monoimide accessory pigments attached to zinc porphyrin. The synthesis, characterization and identification of these arrays for the use as motifs in larger light-harvesting systems are discussed.

Research has been conducted on the ferriprotoporphyrin IX heme mu-oxo dimers and aminoquinolinal antimalarial drugs. The solution structures formed between these compounds at different pH have been investigated via the use of paramagnetic relaxation effects in determining the distance constraints for these solution structures and the details are reported.

Results point out that the presence of the heme b and the absence of a metal histidine bond are involved in the the activation of soluble guanylyl cyclase. Further, the metalloprotein porphyrins serve as activators and are bound 4-coordinate to the enzyme, suggesting that the tetrapyrrole conformation is important.

Research has been conducted on the reaction of 3-phenylbutyraldehyde or 3-phenylpropionaldehyde with P450 (sub) BM3 -F87G carried out in the presence of hydrogen peroxide. The putative isoporphyrin intermediate produced by this reaction has been investigated via the use of the electron paramagnetic resonance spectroscopy and the details are reported.

Research has been conducted on the cofacial biscorroles and linked Co(II) porphyrins and Co(III) corroles. The synthesis and characterization of these compounds with the same face to face orientation are discussed.

Research has been conducted on the manganese-porphyrin catalysts which carry cyclodextrin binding groups. Results indicate that these catalysts can perform hydroxilations with the catalytic turnovers, substrate selectivity and stereo- and regioselectivity.

Research has been conducted on the photochemical dyad. The assembly of this dyad which involves a zinc(II) and a free base porphyrins has been investigated and the results are reported.

Research has been conducted on the iron(III) porphyrin-catalyzed epoxidation reaction. Results indicate that the reactive intermediates responsible for the oxygen atom transfer in these reactions are controlled by the iron(III) porphyrin complexes' anionic ligands.

Research has been conducted on the fullerene complexes. The preparation of fullerene mixed crystals with Co and Zn tetraarylporphyrins carried out in the presence of ferrocene is described.

Research has been conducted on the monocarbaporphyrins. The synthesis, spectroscopic and electrochemical characterization of these compounds are reported and the use of the single-crystal X-ray diffraction in characterizing structurally a carbaporphyrin is described.

Research has been conducted on the murine ferrochetalase. The use of the resonance Raman spectroscopy in investigating interactions of the inhibitor and porphyrin substrates with murine ferrochetalase is discussed.

Research has been conducted on the porphodimethene rearrangements. The methodology of these rearrangements developed to provide chlorin synthesis from pyrrole precursors is described.

Research has been conducted on the cofacial bisporphyrins which are anchored bydibenzofuran and xanthene pillars. The structure, spectroscopy and oxygen atom-transfer reactivity of these bisporphyrins have been investigated and the results are reported.

Research has been conducted on the porphyrin tautomerism. The effect of the steric hindrances on this tautomerism has been investigated via the use of different NMR spectroscopic methods and the details are reported.

Research has been conducted on the pillard cofacial bisporphyrins. The use of the sterically demanding aryl groups opposite the cofacial bridge for tuning the pocket sizes of the pillared bisporphyrins is described.

The authors reviews the publications on chiral lanthanide complexes. The topics of interest include complexes with O-donor ligands, with N-donor ligands, with macrocyclic ligands and enantioselective catalysis by chiral lanthanide complexes.

Research has been conducted on the tetraamine based on pentaerythritol. The synthetic route to this compound has been developed and the results indicate that the access to the pure tetraamine can be facilitated by the tetraazide precursor reduction.

Research has been conducted on the electron configurations in the low-spin iron(III) porphyrin complexes. The role of solvents in these configurations has been investigated and the results are reported.

Research has been conducted on the beta-halogenated and perhalogenated terbium complexes. The synthetic role of these complexes has been investigated and the results are described.

Research has been conducted on the meso, meso-linked porphyrin dimer. The incorporation of this dimer as the light-harvesting chromophore into the photosynthetic electron transfer model in constructing ferrocene-meso, meso-linked porphyrin dimer-fullerene triad is reported.

Tessellation of nine free-base porphyrins into a 3 x 3 array is accomplished by the self-assembly of 21 molecular entities of four different kinds, one central, four corner, and four side porphyrins with 12 trans Pd(II) complexes, by specifically designed and targeted intermolecular interactions. Strikingly, the self-assembly of 30 components into a metalloporphyrin nonamer results from the addition of nine equivalents of a first-row transition metal to the above milieu. In this case each porphyrin in the nonameric array coordinates the same metal such as Mn(II), Ni(II), Co(II), or Zn(II). This feat is accomplished by taking advantage of the highly selective porphyrin complexation kinetics and thermodynamics for different metals. In a second, hierarchical self-assembly process, nonspecific intermolecular interactions can be exploited to form nanoscaled three-dimensional aggregates of the supramolecular porphyrin arrays. In solution, the size of the nanoscaled aggregate can be directed by fine-tuning the properties of the component macrocycles, by choice of metalloporphyrin, and the kinetics of the secondary self-assembly process. As precursors to device formation, nanoscale structures of the porphyrin arrays and aggregates of controlled size may be deposited on surfaces. Atomic force microscopy and scanning tunneling microscopy of these materials show that the choice of surface (gold, mica, glass, etc.) may be used to modulate the aggregate size and thus its photophysical properties. Once on the surface the materials are extremely robust.

Research has been conducted on the manganese tetraphenylporphyrin monoleyer films. The preparation of these films has been carried out and their use as supported oxidation catalysts is described.

Research has been conducted on the electron transfer reactions. The hypothesis coordination of the metal cations can enhance electron transfer rates and the role of the space jumps versus metal-ligand bonds in the electron transfer pathway have been investigated and the details are reported.

Research has been conducted on the cofacial bis-[(porphinato)zinc(II)] compounds. The synthesis, optical spectroscopy and electrochemistry of these compounds have been investigated and the results are reported.

Research has been conducted on the macromolecules. The effect of the macromolecule architecture on the polymeric materials' physical properties has been investigated via the analysis of poly(benzyl ether) dendrons and their linear analogues and the details are presented.

Research has been conducted on zinc porphyrin and 5-[4-(1-hydroxyethyl)phenyl]-10,15,20-triphenylporphyrin. The validity of the transition-state model proposed for the lipase-catalyzed secondary alcohol kinetic resolution has been investigated via the synthesis of these porphyrin compounds and the results are reported.

Research has been conducted on zinc monoethynyl and magnesium monoethynyl porphyrins. The method of obtaining mixed metatalloporphyrin 4,4'-diphenylbutadiyne-linked dyads has been developed and the electronic communication of these dyads have been investigated.

The authors review the publications on interactions of metalloporphyrins with different nitrogen oxides. The topics of interest include the structural aspects of nitrogen oxides with metalloporphyrins.