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BackgroundVDACs (Voltage-Dependent Anion-selective Channels) are pore-forming proteins of the outer mitochondrial membrane, whose permeability is primarily due to their presence. In higher eukaryotes three isoforms raised during the evolution: they have the same exon-intron organization and the proteins show the same channel-forming activity. We provide a comprehensive analysis of the three human VDAC genes (VDAC1–3), their expression profiles, promoter activity, and potential transcriptional regulators.ResultsVDAC isoforms are broadly but also specifically expressed in various human tissues at different levels with a predominance of VDAC1 and VDAC2 over VDAC3. However, RNA-seq CAGE approach revealed a higher level of transcription activation of VDAC3 gene. We experimentally confirmed this information by reporter assay of VDACs promoter activity. Transcription Factor Binding Sites (TFBSs) distribution in the promoters was investigated. The main regulators common to the three VDAC genes were identified as E2FF, NRF1, KLFS, EBOX transcription factors family members. All of them are involved in cell cycle and growth, proliferation, differentiation, apoptosis, and metabolism. More transcription factors specific for each isoform gene were identified, supporting the results in the literature, indicating a general role of VDAC1, as actor of apoptosis for VDAC2, and the involvement in sex determination and development of VDAC3.ConclusionsFor the first time, we propose a comparative analysis of human VDAC promoters to investigate their specific biological functions. Bioinformatics and experimental results confirm the essential role of VDAC protein family in mitochondrial functionality. Moreover, insights about a specialized function and different regulation mechanisms arise for the three isoforms genes.

Voltage-dependent anion channels (VDACs) are a family of pore-forming proteins encoded by different genes, with at least three protein products expressed in mammalian tissues. The major recognized functional role of VDACs is to permit the almost free permeability of the outer mitochondrial membrane (OMM). Although VDAC1 is the best known among VDAC isoforms, its exclusively mitochondrial location is still debated. Therefore, we have measured its co-localization with markers of cellular organelles or compartments in skeletal muscle fibers by single or double immunofluorescence and traditional as well as confocal microscopy. Our results show that VDAC1 immunoreactivity corresponds to mitochondria and sarcoplasmic reticulum, while sarcolemmal reactivity, previously reported, was not observed. Since VDAC1 has been suggested to be involved in the control of oxidative phosphorylation, we sought for possible gene regulation of VDAC1, VDAC2 and VDAC3 in skeletal muscle of the dystrophin-deficient mdx mouse, which suffers of an impaired control of energy metabolism. Our results show that, while VDAC1 mRNA and protein and VDAC2 mRNA are normally expressed. VDAC3 mRNA is markedly down-regulated in mdx mouse muscle at different ages (before, during and after the outburst of myofiber necrosis). This finding suggests a possible involvement of VDAC3 expression in the early pathogenic events of the mdx muscular dystrophy.

Mitochondrial porin, or VDAC, is a pore-forming protein abundant in the outer mitochondrial membrane. Several publications have reported extramitochondrial localizations as well, but the evidence was considered insufficient by many, and the presence of porin in nonmitochondrial cellular compartments has remained in doubt for a long time. We have now obtained new data indicating that the plasma membrane of hematopoietic cells contains porin, probably located mostly in caveolae or caveolae-like domains. Porin was purified from the plasma membrane of intact cells by a procedure utilizing the membrane-impermeable labeling reagent NH-SS-biotin and streptavidin affinity chromatography, and shown to have the same properties as mitochondrial porin. A channel with properties similar to that of isolated VDAC was observed by patch-clamping intact cells. This review discusses the evidence supporting extramitochondrial localization, the putative identification of the plasma membrane porin with the "maxi" chloride channel, the hypothetical mechanisms of sorting porin to various cellular membrane structures, and its possible functions.

A bioptic specimen from the muscles of a patient suffering from severe myopathy was inspected for the presence of human porin 31HL. Western blotting suggested that the specimen was free of the most abundant eukaryotic porin 31HL (HVDAC1). The specimen was treated with detergent and the soluble protein fraction was passed through a dry hydroxyapatite column. The passthrough of this column was inspected for channel formation in artificial lipid-bilayer membranes. The channel observed under these conditions had a single-channel conductance of about 2.5 nS in 1 M KCl, was cation selective, and was found to be virtually voltage independent. Experiments with a control specimen from a healthy human being, without any indication for muscle myopathy, revealed the presence of the voltage-dependent porin 31HL in the sample. It is discussed whether the patient's bioptic specimen contained another human porin, which has not been studied to date in its natural environment.

We have isolated the Drosophila melanogaster gene encoding the mitochondrial acyl carrier protein (mtACP), a subunit of NADH:ubiquinone oxidoreductase involved in de novo fatty acid synthesis in the mitochondrion. This gene expresses two distinct mature transcripts by alternative splicing, which encode mature polypeptides of 86 (mtACP1A) and 88 (mtACP1B) amino acids, respectively. Drosophila mtACP1 is 72% identical to mammalian mtACP, 47% identical to Arabidopsis thaliana mtACP, and 46% identical to Neurospora crassa mtACP. The most highly conserved region encompasses the site that binds pantetheine-4'-phosphate in all known ACPs. Southern analysis of genomic DNA and in situ hybridization to salivary gland chromosomes indicate that a single gene (mtacp1), located at 61F6-8, encodes the two isoforms of D. melanogaster mtACP1. Sequence analysis revealed that the gene contains four exons and that exons IIIA and IIIB are alternatively spliced. A P-element-induced loss-of-function mutation in the mtacp1 gene causes lethality, indicating that the gene is essential for viability. Developmental Northern analysis shows that mtacp1 is expressed at higher levels during late embryogenesis, in the pupa and in the adult. RNA in situ hybridization on embryos indicates that the mtacp1 gene is highly expressed in the tracheal system. Zygotic mtacp1 function is required for both male and female gametogenesis.

Eukaryotic porins or VDACs (Voltage-Dependent Anion-selective Channels) are integral membrane proteins forming large hydrophilic pores. Three functioning genes for VDAC isoforms have been detected in mouse and the corresponding cDNAs are known also in humans. Tissue-specific VDAC isoform 1 (HVDAC1) deficiency in human skeletal muscle is responsible of a rare mitochondrial encephalomyopathy, fatal in childhood. Since coding sequences are not affected in the patient, we focused our interest in the gene structure. HVDAC1 and 2 have been previously mapped at chromosomes Xq13-21 and 21, respectively. Screening of an human chromosome X cosmid library resulted only in the isolation of processed pseudogenes, finely mapped at Xq22 and Xp11.2. Here, we report the mapping of HVDAC1 to chromosome 5q31 and HVDAC2 to chromosome 10q22 by FISH. Exon/intron probes, designed on the basis of the mouse gene structures, were obtained by long extension PCR amplification using the whole genomic DNA as a template. The sequence of the probe extremities clearly pointed to a genuine VDAC genomic sequence. Human and mouse regions where VDAC 1 and 2 genes were mapped are known to be synthetic, thus reinforcing the mapping of the human homologues.

Biotinylated lymphoid cells have been suggested as a useful source of antigen for the immunochemical characterization of their molecular profile. Labelling with biotin eliminates the problems associated with the use of radioactivity. However, this method has not been widely used. This reflects: (1) difficulties in optimizing the signal/background ratio because of the lack of a simple method to quantify biotinylated proteins in a cell lysate, (2) the loss of reactivity with monoclonal antibody of antigen following biotinylation, because of steric hindrance, and (3) the lack of information about the utility of other biotinylated cells as an antigen source. To overcome these limitations, we developed an ELISA to quantify biotinylated proteins in cell lysates and optimized the signal/background ratio. The validity of this approach was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of a number of cell surface antigens immunoprecipitated from lymphoid cells by an optimal amount of monoclonal antibody. Furthermore, we showed that biotinylated melanoma cells are a useful source of antigen for immunoprecipitation experiments and that ligation of biotin to antigen does not affect reactivity with monoclonal antibody. Lastly, biotinylated antigens in cell lysates stored at -80 degrees C for 6 months maintained their reactivity with monoclonal antibodies. Biotinylated cells thus represent a useful source of antigen for characterizing the immunochemical profile and analyzing the specificity of antibodies with immunochemical methods.

In a substantial group of subjects suspected to have a mitochondriopathy no defect in the mitochondrial energy metabolism (pyruvate dehydrogenase complex or respiratory chain complexes) can be demonstrated. At least in some of these subjects it seems justified to consider a defect in one of the proteins which mediate the transport of several ions and substrates across the mitochondrial membranes. Of particular interest are proteins which are directly involved in the process of oxidative phosphorylation, such as the adenine nucleotide translocator (ANT) and the phosphate carrier (PiC). However, defects in transmembrane ion transporters also may induce impaired energy metabolism probably as a result of osmotic disturbances within the mitochondrial matrix. In this respect, the voltage-dependent anion channel (VDAC) and other ion channels have to be taken into consideration. Here we review the still incomplete knowledge of the occurrence of ANT, PiC, VDAC, cation channels, and a few substrate carriers in human tissues, as well as their possible role in pathology.

We have investigated the transmembrane topology of the bovine heart mitochondrial porin by means of proteases and antibodies raised against the amino-terminal region of the protein. The antisera against the human N-terminus reacted with porin in Western blots of NaDodSO4-solubilized bovine heart mitochondria and with the membrane-bound porin in enzyme-linked immunosorbent assay (ELISA). The immunoreaction with mitochondria coated on microtiter wells showed that the amino-terminal region of the protein is not embedded in the lipid bilayer but is exposed to the cytosol. Back-titration of unreacted anti-N-terminal antibodies after their incubation with intact mitochondria demonstrated that the porin N-terminus is also exposed in "noncoated" mitochondria. No difference in antisera reactivity was observed between intact and broken mitochondria. Intact and broken mitochondria were subjected to proteolysis by specific proteases. The membrane-bound bovine heart porin was strongly resistant to proteolysis, but a few specific cleavage sites were observed. Staphylococcus aureus V8 protease gave a large 24K N-terminal peptide, trypsin produced a 12K N-terminal and an 18K C-terminal peptide, and chymotrypsin gave two peptides of Mr 19.5K and 12.5K, which were both recognized by the antiserum against the human N-terminus. Carboxypeptidase A was ineffective in cleaving the membrane-bound porin in both intact and broken mitochondria. Thus, the carboxy-terminal part of the protein is probably not exposed to the water phase. The cleavage patterns of membrane-bound porin, obtained with S. aureus V8 protease, trypsin, and chymotrypsin, showed no difference between intact and broken mitochondria, thus indicating that all porin molecules have the same orientation in the membrane. The computer analysis of the sequence of human B-lymphocyte porin suggested that 16 beta-strands can span the phospholipid bilayer. This result, together with the overall information presented, allowed us to draw a possible scheme of the transmembrane arrangement of mammalian mitochondrial porin.

The deficiency of porin isoform 1 (HVDAC1) in human skeletal muscle has been associated with a pathological phenotype related to defects in the bioenergetic metabolism. In the best studied case, porin deficiency was not apparent in cultured fibroblasts: this observation raised the conclusion that no molecular defect was in the cDNA sequence coding for the protein. To get more insight in the pathogenetic mechanism that is involved in porin isoform 1 deficiency, we have determined the whole structure of the corresponding human gene. On the basis of the corresponding mouse gene structure and the human cDNA sequence, we designed long extension PCR amplifications using the whole genomic DNA as a template. Exonic/intronic regions were isolated and the exons and surrounding introns sequenced. The 5′ and 3′ extremities of the gene were determined by genome walking. The porin isoform 1 human gene is made up of 9 exons and spans about 33 kbp. A whole panel of PCR parameters was set and is now ready to be used for specific amplification upon patients' genomic DNA. The analysis of the putative promoter sequence was performed. It revealed the presence of a sterol Repressor element (SRE), an SRY, the testis-determining factor, and a nuclear respiratory factor 2 (NRF-2) binding site. These sites, according to results from literature, could be involved in the functional modulation of the gene expression.

As a first step towards using cross-species comparison to complete the inventory of the nuclear genes that encode mitochondrial polypeptides, and ultimately to understand their function through systematic molecular and genetic analysis in a model organism of choice, we report here the characterization of 41 Drosophila melanogaster cDNAs. These cDNAs were isolated by screening an ovarian expression library with antibodies against mitochondrial proteins and identify 17 novel Drosophila genes. The deduced amino acid sequences encoded by the majority of these cDNAs turned out to show significant homology to mitochondrial proteins previously identified in other species. Among others, ORFs putatively encoding six different subunits of ATP synthase and three NADH:ubiquinone reductase subunits were detected. By in situ hybridization, all cDNAs were mapped to single bands on polytene chromosomes, thus identifying candidate Drosophila genes required for mitochondrial biogenesis and maintenance. A search of the Human Gene Index database made it possible in most cases to align the entire Drosophila coding sequence with a human consensus sequence, suggesting that the cDNAs originate from insect counterparts of expressed mammalian genes. Our experimental strategy represents an efficient approach to the identification and interspecies comparison of genes encoding products targeted to the mitochondrion.

Motivations. The species subject of our work belong to different orders of Teleosts, one of which is the order of Clupeiformes consisting in two large families of commercial interest (Clupeidae and Engraulidae), which include the small fish commonly known, respectively, for herring, sardines, shads, and sprats and anchovies. Their molecular identification is useful because a common fraud is their species replacement. In addition, because of globalization, it is possible to find in our markets also other species of anchovy typical of different distribution areas, such as Japanese anchovy (Engraulis japonicus), the Peruvian Anchovy (E. ringens), the Atlantic Ali (E. anchoita) and the Californian anchovy (E. mordax). Due to the differentiation of the processed foodstuffs that characterizes the market, it is essential to develop tools for unequivocal and quick identification of the species present in the market even when morphological identification is no longer possible. Methods. DNA barcoding consists of the utilization of short DNA sequences to identify organisms, in particular the species. The quest for a genetic marker useful to determine unambiguously the species is still a matter of debate. For animals, the best candidate to this role has been proposed to be the citochrome oxidase I (COI) gene. In vertebrates the mtCOI gene is 1545 bp long, a region of 648 bp close to the beginning of the translated sequence is properly said to be the "barcode". We applied the DNA barcoding technologies, upon a segment of COI to compare fish belonging to Clupeiformes order and the analysis of 5'Dloop sequences to stock identification [1]. The fish was used for extracting genomic DNA, amplifying and sequencing. The sequences obtained were aligned using ClustalX. Relationships among the sequence obtained were examined using Neighbour-joining (NJ) and Bayesian analyses. The NJ tree was constructed using pairwise distances calculated following the application of Kimura's two-parameter (K2P) correction for multiple substitutions in MEGA v. 4.0. The robustness of internal branches of distance was estimated by bootstrapping with 1000 replicates. Modeltest v. 3.06 was used to select the most appropriate models of sequence evolution for the Bayesian analysis that was implemented in MrBayes v. 3.0 using a Metropolis-coupled, Markov Chain Monte Carlo (MCMC) sampling approach. The DNA Barcoding procedure produces a whole catalogue of I.D. of individual species or populations of fish. A key service for the utilization of analytical data is the organization of a BioBank collecting biological samples, DNA samples, genomic sequences connected also to a Knowledge base that represents sequence collected and is capable to interact with remote databases. The knowledge base will be equipped with a data mining module providing advanced tools to automatically extract new knowledge by highlighting predictive patterns of interest [2]. Results. Our results allow the molecular identification of the fish (through the COI) also in its processed product, and in some case the identification of the geographical origin of the specific fish (through the 5'Dloop). Genetic analysis of the species of interest, are conducted through the innovative technique of DNA Barcoding alone or in combination with the high-resolution melting analysis (HRM) analysis, called Bar-HRM (High Resolution Melting-barcode DNA). This will allow to increase the knowledge of species not yet well studied, but of considerable importance for the Mediterranean area. The genetic analysis of the species of interest are exploited not only for the recognition of species-specific sequences, i.e. the ability to distinguish between two organisms belonging to different species, but also for determining the provenance of the fish (characterization of fish stock). References 1. A.M. Pappalardo, F. Guarino, S. Reina, A. Messina and V. De Pinto Geographically widespread swordfish barcode stock identification: a case study of its application (2011) PLOS ONE, doi: 10.1371/journal.pone.0025516 2. A. Lagana, S. Forte, A. Giudice, M. R. Arena, P. L. Puglisi, R. Giugno, A. Pulvirenti, D. Shasha, Ferro A. (2009). miRo: a miRNA knowledge base. DATABASE, vol. Vol. 2009, bap008; p. *, ISSN: 1758-0463, doi: 10.1093/database/bap008

The role of positive charges located on the hydrophilic surface of the mitochondrial outer membrane channel was investigated by studying the interaction between LDAO-solubilized porin and a cation-exchanger column. The binding of porin to the column material was inhibited when the elution buffer had a pH of 9 or when 2 mM dextran sulfate was added to the buffer at neutral pH. Interestingly, the addition of a synthetic copolymer of methacrylate, maleate and styrenc known as a potent modulator of the voltage-dependence, did not influence the interaction between column material and porin. Incubation of porin with fluorescein isothiocyanale (FITC) resulted in the isolation of a porin fraction in which on average two lysines located on the surface of the pore-forming complex per 35 kDa polypeptide were modified. The voltage-dependence of the fluorescein isothiocyanate modified porin was strongly decreased as compared with the unmodified porin. The experiments presented here give the first biochemical evidence that positively charged lysine residues located on the surface of the channel-forming complex are responsible for the gating of the mitochondrial porin-channel.

The remineralization of phytoplankton-bound phosphorus subsequent to nonpredatory phytopiankton mortality represents a significant source of algal-available phosphorus in many lakes. A unique experimental apparatus (A Dual Culture Diffusion Apparatus) was used to measure the rate and extent of this process and to elucidate some of the governing factors. It was demonstrated that this process is strongly influenced by heterotrophic decomposer activity, because phosphorus regeneration rates were less than 0.01/d for cultures not inoculated with a decomposer community, while they were two to five times higher for decomposer-inoculated cultures. In addition to the character and activity of the microbial decomposer community, the phytoplankton cell phosphorus content was shown to be a significant factor in the rate of phosphorus regeneration for a given cell decay rate. Cell phosphorus above the minimum cell quota appeared to be released in an available form quite rapidly upon algal death and lysis.

A new, simple and rapid procedure for the purification of high amounts of mitochondrial porins from different tissues of mammalia is described. The method consists in a single step hydroxyapatite / celite chromatography of Triton X-100 solubilized mitochondrial membranes. For optimal purification several factors are critical such as the absence of salts, a low protein / detergent ratio and an exact hydroxyapatite / celite ratio of 2:1.

The effect of different families of detergents on the solubilization and purification of the pore-forming protein (porin) of the mitochondrial outer membrane of bovine heart was investigated in detail. With Tritons, dimethylamine oxides and zwittergents, porin solubilization with respect to total mitochondrial membrane protein was more efficient with the more hydrophobic members of each series. With most detergents the protein eluted as protein-detergent micelles in the void volume of hydroxyapatite/celite columns. In contrast, the protein was bound to the column material and was eluted after the addition of salt to the elution buffer when the detergents octylglucoside, zwittergent Z-314 and lauryl(dimethyl)-amine oxide were used. The protein purified in the presence of the latter detergent had a higher pore-forming activity in lipid bilayer membranes compared to porin isolated in the presence of Triton X-100. The binding of porin to the hydroxyapatite/celite column was used to study the lipid content of the active pore-forming complex. The analysis revealed that the complex contained no phospholipid but rather five molecules of cholesterol/polypeptide chain.

The mitochondrial porins from mammalian tissues and from low eukaryotic cells were purified with a high yield, and their biochemical and functional properties were investigated. When analyzed by SDS gel electrophoresis, all mammalian porins show a very similar apparent molecular mass (35–35.5 kDa). In contrast yeast and Paramecium porins have a molecular mass of 30 and 37 kDa, respectively. The peptide maps of mammalian porins are very similar although small differences are apparent between porins of different tissues of the same organism and also between those of the same tissue of different organisms. The peptide patterns of porins from yeast and Paramecium are completely different from those of mammalian porins. Antibodies raised against the rat liver porin cross-react with all the other mammalian porins but not with that of yeast. The incorporation of porins into artificial lipid bilayer membranes showed that they are able to form pores with approximately the same specific activity. The single-channel conductance is for all porins, except for that of Paramecium , about 4 nS in 1 M KCI, corresponding to an effective pore diameter of 1.7 nm. They are voltage-dependent and switch to substates at transmembrane potentials higher than 10 mV. The number of gating charges varies, however, for pores from different tissues, indicating a different sensitivity to the potential as a result of a possible different function.

Mitochondrial porin was isolated from the fruit fly Drosophila melanogaster at different developmental stages, starting from whole mitochondria. The porin from adults' mitochondria was fully characterized. The protein had a molecular mass of 31 kDa as judged from sodium dodecylsulfate electrophoretograms. It was very resistive against digestion with V8 proteinase of Staphylococcus aureus and a larger number of fragments were only obtained after digestion with papain. Drosophila porin showed little interaction with antibodies raised against mitochondrial porins from mammalia and Neurospora crassa , but a strong reactivity with antibodies raised against yeast porin. Reconstitution experiments with planar lipid bilayer membranes showed that the protein was able to form ion-permeable pores with a single-channel conductance of 0.41 nS in 0.1 M KCl. At low transmembrane voltages Drosophila poril had the properties of a general diffusion pore with an estimated effective diameter of about 1.7 nm and a small selectivity for anions over cations. Voltages larger than 20 to 30 mV resulted in a closure of the pore. The closed states of the pore were found to be cation-selective. The addition of a synthetic polyanion to the aqueous phase on one side of the membrane resulted in an asymmetric shift of the voltage dependence and the pore became already closed at very small voltages negative at the cis-side (the side of the addition of the polyanion).

Glutamate dehydrogenase has been purified to near-homogeneity from mature larvae of Drosophila melanogaster. The enzyme has a molecular weight of 347,000 measured by sucrose gradient sedimentation and 343,000 measured by variable-porosity acrylamide gel electrophoresis. Electrophoresis under denaturing conditions showed that the enzyme consists of six subunits of molecular weight 57,000. The structural gene for GDH has been mapped at 81.7 +/- 0.8 on the third chromosome by means of an electrophoretic variant.

The methods for the purification of functionally active mitochondrial porin or voltage-dependent anion channel of the outer mitochondrial membrane are critically evaluated. Two rapid and efficient methods are now available. Both make use of a hydroxyapatite/celite column as a single chromatographic step. However, in one method with long polar head-group detergents, porin passes through the column, whereas in the other method, with shorter polar head-group detergents, porin is first bound to the column and then eluted by the addition of salts. On the basis of these results, a model for the arrangement of porin in the detergent-protein micelles is proposed.

Glutamine synthetase II was purified from Drosophila melanogaster adults. It was completely separable from the isozyme glutamine synthetase I by means of DEAE chromatography. The complete enzyme has an apparent molecular weight of 360,000. After two-dimensional electrophoresis it gave a single molecular species with an apparent molecular weight of 42,000. Structural analysis of the two isozymes showed that they are different both in subunit molecular weight and in isoelectric point. Peptide maps of the purified subunits showed considerable dissimilarity. Glutamine synthetase II is more active than glutamine synthetase I in the transferase assay, while the opposite is true in the biosynthetic assay. The kinetic parameters were determined, showing again noteworthy differences between the two isozymes. We therefore conclude that two forms of glutamine synthetase are present in Drosophila, with different primary structures, different kinetic behavior, and the possibility of different functional properties.

The general procedure for the isolation of the phosphate carrier from mitochondria involves solubilization with non-ionic detergents and chromatography on hydroxylapatite [l-3]. With high resolution SDS-gel electrophoresis this preparation can be separated into 4-5 protein bands [2]. Further purification, in particular removal of the ADP/ATP-carrier, was obtained by chromatography on Celite [2], on Mersalyl-Ultrogel [3,4] and by using Triton X-l 14 instead of Triton X-100 [5]. However, after all these procedures the purified phosphate carrier fraction still contained 4-5 protein bands in the &.-region of 30 000-35 000 [5]. Affi-Gel 501 (an organomercurial agarose gel), Dowex AG l-X8 and hydroxylapatite (Bio-Gel HTP) were obtained from Bio-Rad; [32P]phosphate (carrier free) from Amersham; [3H]NEM from New England Nuclear; acrylamide, N,N’methylenebisacrylamide, SDS, Triton X-100 and NEM from Serva; scintillation liquid (Maxifluor) from J. Baker; L-cY-phosphatidylcholine (from egg yolk, Type X-E) from Sigma and cardiolipin from Serdary.

The mitochondrial porin or VDAC (Voltage-Dependent Anion Channel), the pore-forming structure responsible for the high permeability of the outer mitochondrial membrane, was found to be one of only three mitochondrial proteins bound by [14C]dicyclohexylcarbodiimide (DCCD) at low dosages (1.5 nmol/mg of mitochondrial porin) (De Pinto, V., Tommasino, M., Benz, R., and Palmieri, F. (1985) Biochim. Biophys. Acta 813, 230-242). Treatment of intact mitochondria with DCCD results in the inhibition of their ability to binding hexokinase (Nakashima, R. A., Mangan, P. S., Colombini, M., and Pedersen, P. L. (1986) Biochemistry 25, 1015-1021). In the present study, mitochondrial porin was purified from [14C]DCCD-labeled mitochondria. The purified labeled porin was treated with the cleavage reagent CNBr and with the endoproteases trypsin and V8 from Staphylococcus aureus and blotted to polyvinylidene difluoride membrane. The transferred peptides were detected with Coomassie Blue dye, excised, and sequenced. The sequences of several labeled and unlabeled peptides were obtained and then overlapped. The region containing the [14C]DCCD radioactivity was limited to 50 amino acid residues and completely sequenced. Covalently incorporated [14C]DCCD was exclusively released at the position corresponding to glutamate 72. The DCCD-reactive residue is located in the 4th of 16 predicted transmembrane amphipathic beta-strands. When the sequence surrounding the DCCD site was compared to those surrounding the DCCD-reactive residue of other membrane proteins, no homology was apparent.

Mitochondrial porin from corn (Zea mays L. B 73) shoots was solubilized with lauryl(dimethyl)-amine oxide and purified by chromatography on a hydroxyapatite:celite column. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the purified protein had an apparent molecular mass of 35 kD. When reconstituted in planar lipid bilayer membranes the porin formed ion-permeable channels with single-channel conductance of 2.0 and 4.0 nanosiemens in 1 M KCl. At low transmembrane voltages corn porin had the properties of a general diffusion pore with an estimated effective diameter of 1.6 nm and a small selectivity for anions over cations. The primary structure of corn porin seems to be quite different from that of other mitochondrial porins, because it did not cross-react with monoclonal antibodies against human porin and with polyclonal antibodies against yeast porin. Furthermore, the peptide maps of corn and bovine heart porins were very different. A sequence of 21 amino acids obtained by Edman degradation of peptides generated by porin proteolysis with Staphylococcus aureus V8 protease did not show any significant homology with known sequences of mitochondrial porins. Results of our investigation suggest that corn porin possesses functional properties similar to those of other mitochondrial porins, despite major structural differences.

• A small percentage of paraplegic patients develop chronic decubitus ulcers that are unresponsive to the usual plastic surgical maneuvers. We used anatomic and nonanatomic (filleting) approaches to hip disarticulation in three patients with severe chronic cavernous decubitus ulcers. All patients were rehabilitated to wheelchair ambulation, with subsequent healing of the operative sites. This type of therapy might be considered in paraplegics with less compelling reasons for amputation, because of the associated rehabilitation potential. ( Arch Surg 1987;122:1040-1043)