Cytochromes, rubredoxin, and sulfur metabolism of the non-thiosulfate-utilizing green sulfur bacterium Pelodictyon luteolum

Abstract

Two soluble c-type cytochromes (c-553 and c-555) and the nonheme iron-containing protein rubredoxin of the non-thiosulfate-utilizing green sulfur bacterium Pelodictyon luteolum were highly purified by ion exchange column chromatography, gel filtration and ammonium sulfate fractionation. Both cytochrome are small and basic hemoproteins, while rubredoxin is an acidic small nonheme iron protein. Cytochrome c-553 has a molecular weight of 13,000 determined by Sephacryl S-200 chromatography and of 10,700 by electrophoresis on SDS acrylamide gel, an isoelectric point at pH 10.2, a redox-potential of +220 mV. It shows maxima at 413 nm in the oxidized form, and the characteristic three maxima in the reduced state (α-band at 553 nm, β-band at 523 nm, γ-band at 417 nm). The best purity index (A280/A417) obtained was 0.18. Cytochrome c-555 (best purity index obtained: A280/A418=0.17) has an isoelectric point at pH 10.5, a molecular weight of 9,500 (by electrophoresis on SDS acrylamide gel) and a redox-potential of +160mV. The reduced form of this cytochrome shows the typical bands of c-type cytochromes at 555 (551) nm (α-band), 523 nm (β-band) and 418 nm (γ-band), while the oxidized form has the γ-band at 413 nm.