BACILLUS-SUBTILIS CTAA AND CTAB FUNCTION IN HEME-A BIOSYNTHESIS

Haem A, a prosthetic group of many respiratory oxidases, is probably synthesized from haem B (protohaem IX) in a pathway in which haem 0 is an intermediate. Possible roles of the Bacillus subtilis ctaA and ctaB gene products in haem 0 and haem A synthesis were studied. Escherichia coli does not contain haem A. The ctaA gene on plasmids in E. coli resulted in haem A accumulation in membranes. The presence of ctaB together with ctaA increased the amount of haem A found in E. coli. Haem 0 was not detected in wild-type B. subtilis strains. A previously isolated B. subtilis ctaA deletion mutant was found to contain haem B and haem 0, but not haem A. B. subtilis ctaB deletion mutants were constructed and found to lack both haem A and haem 0. The results with E. coli and B. subtilis strongly suggest that the B. subtilis CtaA protein functions in haem A synthesis. It is tentatively suggested that it functions in the oxygenation/oxidation of the methyl side group of carbon 8 of haem 0. B. subtilis CtaB, which is homologous to Saccharomyces cerevisiae COX10 and E. coli CyoE, also has a role in haem A synthesis and seems to be required for both cytochrome a and cytochrome o synthesis.