EFFECT OF OXYGEN ON CYTOCHROME PATTERN AND HEME SYNTHESIS IN ESCHERICHIA COLI

Abstract

Aerobically grown cells of Escherichia coli contained several times as much cytochrome b₁, cytochrome d, and protoheme as anaerobically grown cells. The activity for the synthesis of δ-aminolevulinic acid (ALA) from succinate and glycine was remarkably higher in aerobically than in anaerobically grown cells. Incubation of anaerobically grown cells for 4hr with ALA under either aerobic or anaerobic condition resulted in the synthesis of protoheme, but the aerobic incubation was more favorable for the heme formation. By prolonged aeration of anaerobically grown cells with ALA, porphyrins were accumulated inside and outside of the cells. If casamino acids were supplemented to the incubation mixture containing ALA, the aerobic protoheme formation was much more pronounced, and the heme synthesis was partly inhibited by chloramphenicol and by puromycin. Accompanied with the formation of protoheme by the aerobic incubation of anaerobically grown cells, a cytochrome-type pigment, which could be reduced by succinate or NADH and oxidized by air, accumulated in the cells. The reduced spectrum of the pigment showed peaks identical with those of cytochrome b₁, but the shape of the absorption curve was not the same as that of the cytochrome.
These results, and previous findings, reveal that the effect of oxygen on the formation of heme and cytochrome in E. coli is manifold; oxygen enhances (1) the formation of enzymes for succinyl-CoA synthesis, (2) formation of enzymes in some step between ALA and protoheme, (3) the reaction of preformed enzymes in some step between ALA and protoheme (probably the conversion of coproporphyrinogen to protoporphyrin), and possibly (4) the formation of ALA synthetase. In addition, oxygen may affect the formation of apoprotein moiety of cytochromes.