Interrelations Between Two Pathways of Methionine Biosynthesis in Aerobacter aerogenes

SUMMARY Two pathways for methionine methyl formation, one cobalamin-dependent and one cobalamin-independent, corresponding to those observed in Escherichia coli pa 15 have been found in Aerobacter aerogenes. An initial difficulty in showing the cobalamin-dependent pathway in cell-free extracts proved to be due to the presence of enzymes which caused the removal of adenosylmethionine, a cofactor required for this system. In contrast to E. coli pa 15, A. aerogenes contains holocobalaminmethyl-transferase even when grown in the absence of cobalamin. When cobalamin is added to the growth medium, the cobalamin-independent pathway is repressed.