Reduction of iron and synthesis of protoheme by Spirillum itersonii and other organisms

Abstract

Membranes from S. itersonii reduce ferric iron to ferrous iron with NADH or succinate as a source of reductant. Iron reduction was measured spectrophotometrically at 562 nm using ferrozine, which chelates ferrous iron specifically. NADH or succinate was effective as a source of reductant for synthesis of protoheme with ferric citrate as a source of Fe. The effects of respiratory inhibitors suggested that reduction of Fe occurs at .gtoreq. 1 sites on the respiratory chain before cytochrome c. Reduction of Fe and synthesis of protoheme with the physiological reductants were observed with crude extracts of other bacteria, including Rhodopseudomonas spheroides, R. capsulata, Paracoccus denitrificans and Escherichia coli. The effect of O2 on reduction of Fe and formation of protoheme was examined with membranes from S. itersonii, using succinate as a source of reductant. Both systems were inhibited by O2, but this effect was completely reversed by addition of antimycin A. Reduced components of the respiratory chain apparently serve as reductants for ferric iron, but with O2 present they are oxidized preferentially by the successive members of the chain. This could be a mechanism for regulating synthesis of heme and cytochrome by O2.