INFLUENCE OF BIOLOGICAL METHYLATION ON THE BIOSYNTHESIS OF MITOMYCIN A

Abstract

Methionine-methyl-C14 was shown to contribute radio-active carbon to the mitomycin antibiotic complex synthesized by Streptomyces verticillatus in a simple synthetic medium containing glucose and inorganic salts. The position of radioactivity in mitomycin-A was determined by selective hydrolysis of the 7 and 9a methoxyl functions. Essentially all of the radioactivity incorporated was distributed evenly between these two substituent groups. Mitomycin-A, synthesized by washed resting cells of S. verticillatus at the expense of internal metabolites, also incorporated methyl label. When the methionine antagonist, D, L-ethionine, was added to resting cells at a concentration causing 65% inhibition of antibiotic synthesis, incorporation of radioactive methyl groups was reduced to the same extent. Synthetic medium supplemented with D, L-ethionine supported about 90% maximal growth of the culture, but antibiotic biosynthesis was markedly inhibited. The addition of the inhibitor during the period of rapid antibiotic synthesis resulted in cessation of further increases in antibiotic titer. L-Methionine was shown to be capable of reversing ethionine inhibition; The extent of reversal was dependent on the concentration, as well as on the time of addition of amino-acid. The data suggest the critical nature of a methyl transfer system in the biogenesis of biologically active mitomycins.