Cytochrome c3 and Desulphoviridin; Pigments of the Anaerobe Desulphovibrio desulphuricans

SUMMARY: Suspensions of various mesophilic strains of Desulphovibrio desulphuricans show absorption bands attributable to a cytochrome and a green protein; there are small differences in the position of absorption maxima depending on the strain and culture medium. Both pigments have been extracted, together with flavins rich in flavinadenine dinucleotide; an electrophoretically and chromatographically pure preparation of the cytochrome has been obtained and is designated c 3. The green protein has been termed ‘desulphoviridin’. Cytochrome c 3 is a soluble autoxidizible thermostable haemoprotein (reduced bands at 553, 525 and 419 mμ.) of low redox potential ( − 205 mV.), high iso-electric point (pH >10) and containing 0·9 %Fe. Degradation studies indicate that it is a bifunctional haemato-haematin with the thio-ether haem-apoprotein links also found in cytochromes c and f; its m.w. is approx. 13,000 (S20,w = 1·93 × 10−13). Spectroscopic data for various derivatives including haemin c 3 and a porphyrin derivative are recorded. Material purified to at least 94 % by cellulose and ion-exchange chromatography acts as carrier in the reduction in hydrogen of sulphite, thiosulphate, tetra-thionate or dithionite by detergent-treated bacterial preparations; a similar role has been demonstrated with cell-free systems which reduce sulphite, thiosulphate and tetrathionate. Benzylviologen would replace cytochrome c 3. No preparation has been obtained showing c 3-linked sulphate reduction; the evidence for this depends on difference spectra and competition by known sulphate antagonists. Oxidation of H2 or organic compounds with O2 has been demonstrated with these bacteria; the H2/O2 reaction takes place fastest in an atmosphere containing 4 % O2, when oxygen is frequently reduced faster than sulphate. The reaction requires the mediation of cytochrome c 3 and is probably a consequence of the autoxidizibility of c 3. Desulphoviridin is a thermolabile, soluble, acidic porphyroprotein absorbing at 630, 585 and 411 mμ.; no metabolic function has been detected. It is stable over a limited pH range and decomposes readily, yielding a chromophoric group which fluoresces red in ultraviolet light, absorbs at 595 mμ. in neutral and alkaline solution (solution red) and at 612 mμ. in acid solution (solution blue-green). This material can be purified by chromatography on ‘Florisil’ or paper. It is very photo-sensitive and water-soluble. Its character is obscure; it may be a highly carboxylated chlorin. Spectroscopic data are recorded.