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A study was conducted to examine the nucleotide sequence of the hydA and hydB genes that encode the [Fe] hydrogenase from Desulfovibrio desulfuricans ATCC 7757. The deduced amino acid sequence of the genes was found to be similar to that of D. vulgaris, a closely related specie. A carboxy-terminal processing of the large subunit that involve the cleavage of a 24-residue peptide was also observed. These results suggest that the C-terminal plays a role in the transport of the protein to the periplasm.

The properties of the periplasmic hydrogenase from Desulfovibrio desulfuricans ATCC 7757, previously reported to be a single-subunit protein [Glick, B. R., Martin, W. G. and Martin, S. M. (1980) Can. J. Microbiol. 26, 1214–1223] were reinvestigated. The pure enzyme exhibited a molecular mass of 53.5 kDa as measured by analytical ultracentrifugation and was found to comprise two different subunits of 42.5 kDa and 11 kDa, with serine and alanine as N-terminal residues, respective- ly. The N-terminal amino acid sequences of its large and small subunits, determined up to 25 residues, were identical to those of the Desulfovibrio vulgaris Hildenborough [Fe]-hydrogenase. D. desulfuricans ATCC 7757 hydrogenase was free of nickel and contained 14.0 atoms of iron and 14.4 atoms of acid-labile sulfur/molecule and had ε400, 52.5 mM-1 · cm-1. The purified hydrogenase showed a specific activity of 62 kU/mg of protein in the H2-uptake assay, and the H2-uptake activity was higher than H2-evolution activity. The enzyme isolated under aerobic conditions required incubation under reducing conditions to express its maximum activity both in the H2-uptake and 2H2/1H2 exchange reaction. The ratio of the activity of activated to as-isolated hydrogenase was approximately 3. EPR studies allowed the identification of two ferredoxin-type [4Fe-4S]1+ clusters in hydrogenase samples reduced by hydrogen. In addition, an atypical cluster exhibiting a rhombic signal (g values 2.10, 2.038, 1.994) assigned to the H2-activating site in other [Fe]-hydrogenases was detected in partially reduced samples. Molecular properties, EPR spectroscopy, catalytic activities with different substrates and sensitivity to hydrogenase inhibitors indicated that D. desulfuricans ATCC 7757 periplasmic hydrogenase is a [Fe]-hydrogenase, similar in most respects to the well characterized [Fe]-hydrogenase from D. vulgaris Hildenborough. [ABSTRACT FROM AUTHOR]

1. The antimycin binding sites were found to be independent of cytochrome(s) b synthesis in pseudo-wild-type revertants of cytochrome b mutants. These revertants, whose primary mutation is located in the introns of the cob-box gene of mitochondrial DNA, have modified contents of cytochromes b-562 and b-565 and fully functional respiratory chain. 2. Missense mutations in three genetic loci allocated to the exons of the cytochrome b gene, abolish the strong affinity binding of antimycin. 3. It is proposed that the antimycin-binding component is not cytochrome b itself, but interacts with it in such a way that an alteration of the cytochrome b structure affects the antimycin-binding site. [ABSTRACT FROM AUTHOR]