Two enzymes for oxygen-dependent and independent decarboxylation of coproporphyrinogen III during bacterial tetrapyrrole biosynthesis

Abstract

During the biosynthesis of hemes and chlorophylls coproporphyrinogen 111 oxidase decarboxylates coproporphyrinogen I11 to form protoporpyhrinogen IX. In eucaryotes almost exclusively an oxygen-dependent enzyme is found. Due to anaerobic growth environments bacteria possess two structurally not related enzymes, again the oxygen-dependent HemF and the oxygen-independent HemN. Both enzymes from Escherichia coli were biochemically characterized after recombinant production and chromatographic purification. Oxygen-dependent HemF requires histidine coordinated manganese. Oxygen-independent H e m N carrying an iron-sulphur-cluster requires S-adenosyl methionine, NAD(P)H and an unknown cytoplasmic component for activity. Similarities with enzymes using radical mechanisms are obvious.16 Mechanistic insights into flavocytochrome c3, the soluble fumarate reductase from Shewanella frigidimarina.