Electronic properties of the dissimilatory sulphite reductase from Desulfovibrio vulgaris (Hildenborough): comparative studies of optical spectra and relative reduction potentials for the [Fe4S4]-sirohaem prosthetic centres

Abstract

The dissimilatory sulphite reductase (desulfoviridin) from the sulphate-reducing bacterium Desulfovibrio vulgaris (Hildenborough) displays distinct optical and redox characteristics relative to the haem subunit of Escherichia coli assimilatory sulphite reductase. For high-spin pentaco-ordinate desulfoviridin there is minimal change in the absorbance of the oxidized chromophores both after reduction or after addition of exogenous ligands. A ligand-metal charge-transfer band approximately 702 nm is observed in both the oxidized and one-electron-reduced enzyme. E.p.r. spectroscopy has been used to define the relative reduction potentials for sirohaem and [Fe4S4] centres (delta E0 = Es0-Ec0) as a function of sirohaem axial co-ordination. Typically delta E0 lies in a range from -10 to -50 mV. These results show a correlation with the sigma-donor or pi-acceptor properties of the ligand and stand in sharp contrast with estimates for the E. coli enzyme. The electronic properties of the coupled [Fe4S4]-sirohaem redox centre common to both nitrite- and sulphite-reducing enzymes are apparently strongly dependent on the environment generated by protein side chains.

Models of the Bis-Histidine-Ligated Electron-Transferring Cytochromes. Comparative Geometric and Electronic Structure of Low-Spin Ferro- and Ferrihemes

“…The cytochromes b, all of which contain heme b (also called protoheme or iron protoporphyrin IX), are found in the bc 1 complex of mitochondrial inner membranes of animals, [17][18][19][20][21][22][23] yeast, 24,25 bacteria, 26,27 algae, photosynthetic bacteria, [28][29][30] and the b 6 f complex of chloroplasts, 17,[31][32][33] as well as in liver microsomes, 34 outer mitochondrial membranes, 35 and erythrocytes, 36 and in certain enzymes such as sulfite oxidase, 37 sulfite, [38][39][40] nitrite [41][42][43][44][45][46] and nitrate [41][42][43][44][45][46] reductases, lactate dehydrogenase flavocytochrome b 2 , 47,48 succinate:quinone oxidoreductase (SQR, also known as succinate dehydrogenase, and, for eukaryotes, as mitochondrial Complex II; however, not all of the SQR enzymes contain heme), 49 the related enzyme for the backward reaction, quinol:fumarate reductase (QFR, not all of which contain heme 50 ), [51][52]…”

“…The cytochromes b , all of which contain heme b (also called protoheme or iron protoporphyrin IX), are found in the bc 1 complex of mitochondrial inner membranes of animals, − yeast, , bacteria, , algae, photosynthetic bacteria, − and the b 6 f complex of chloroplasts, ,− as well as in liver microsomes, outer mitochondrial membranes, and erythrocytes, and in certain enzymes such as sulfite oxidase, sulfite, − nitrite − and nitrate 41-46 reductases, lactate dehydrogenase flavocytochrome b 2 , , succinate:quinone oxidoreductase (SQR, also known as succinate dehydrogenase, and, for eukaryotes, as mitochondrial Complex II; however, not all of the SQR enzymes contain heme), the related enzyme for the backward reaction, quinol:fumarate reductase (QFR, not all of which contain heme), − and formate dehydrogenase-N . A number of these cytochromes, including cytochrome b 5 (found in liver microsomes, outer mitochondrial membranes, and erythrocytes 36 ), bacterial cytochromes bc 1 26 and c 3 , − cytochromes bc 1 ( b 562 and b 566 , or b H and b L ), − …”

Synthesis of a [Fe4S4]−S−Ferriheme Bridged Assembly Containing an Isobacteriochlorin Component: A Further Analogue of the Active Site of Sulfite Reductase

“…There are, however, sufficient cysteinyl residues (seven or eight) 7c to provide the four cysteinyl ligands of the cluster. The dissimilatory SiR from D. vulgaris also carries a coupled siroheme-cluster entity, but the nature of the bridge is unknown.…”

Key Bacterial Multi-Centered Metal Enzymes Involved in Nitrate and Sulfate Respiration

“…SiRs are important constituents of the respiratory electron transfer chain in sulfate-reducing bacteria and catalyze the sixelectron reduction of sulfi te to sulfi de [see Thauer et al, 1977] SiR has been described as ␣ 2 ␤ 2 ␥ m ␦ n multimers with ␣ ; 50 kDa, ␤ ; 45 kDa, ␥ ; 11 kDa, ␦ ; 8 kDa, and a total molecular mass of approximately 200 kDa [Steuber and Kroneck, 1998]. The enzyme has been isolated from several organisms including A. fulgidus [Dahl et al, 1990Lee et al, 1971Lee et al, , 1973Lui et al, 1994;Moura et al, 1988]. The structure of the ␥ -subunit from Pyrobaculum aerophilium as well as the ␦ -subunit from D. vulga ris has been characterized most recently.…”