IN-VITRO HEME O SYNTHESIS BY THE CYOE GENE-PRODUCT FROM ESCHERICHIA-COLI

The cytochrome bo complex is a heme-copper terminal quinol oxidase in the aerobic respiratory chain of Escherichia coli and contains low spin heme B, high spin heme O and CU(B) as the redox metal centers in subunit I. Based on site-directed mutagenesis studies on the cyoE gene in the cytochrome bo operon, we have postulated that the cyoE gene encodes a protoheme IX farnesyltransferase (heme O synthase) (Saiki, K., Mogi, T., and Anraku, Y. (1992) Biochem. Biophys. Res. Commun. 189, 1491-1497). The present study demonstrates that the CyoE protein is localized in the cytoplasmic membrane and that the CyoE-overproduced membranes efficiently catalyze a conversion of exogenous ferrous protoheme IX and farnesyl diphosphate to heme O in the presence of divalent cations such as Mg2+ or Ca2+. Thus, the cyoABCDE operon in E. coli encodes not only subunits of the cytochrome bo complex but also heme O synthase that is specifically required for functional expression of the bo-type quinol oxidase. Heme O seems to be an intermediate in heme A biosynthesis.