BACILLUS-SUBTILIS-CTAA IS A HEME-CONTAINING MEMBRANE-PROTEIN INVOLVEDIN HEME-A BIOSYNTHESIS

Heme A is a prosthetic group of many respiratory oxidases. It is synth esized from protoheme IX (heme B) seemingly with heme O as a stable in termediate. The Bacillus subtilis ctaA and ctaB genes are required for heme A and heme O synthesis, respectively (B. Svensson, M. Lubben, an d L. Hederstedt, Mol. Microbiol. 10:193-201, 1993). Tentatively, CtaA is involved in the monooxygenation and oxidation of the methyl side gr oup on porphyrin ring D in heme A synthesis from heme B. B. subtilis c taA and ctaB on plasmids in both B. subtilis and Escherichia coli were found to result in a novel membrane-bound heme-containing protein wit h the characteristics of a low-spin b type cytochrome. It fan be reduc ed via the respiratory chain, and in the reduced state it shows light absorption maxima at 428, 528, and 558 nm and the or-band is split. Pu rified cytochrome isolated from both B. subtilis and E. coli membranes contained one polypeptide identified as CtaA by amino acid sequence a nalysis, about 0.2 mol of heme B per mol of polypeptide, and small amo unts of heme A.