Metabolism of 2,6-diaminopurine: S-adenosylmethionine as methyl donor for 2-methylamino-6-aminopurine synthesis.

Previous studies (1, 2) have demonstrated that resting cell suspensions of Escherichia coli B not only incorporate 2,6diaminopurine into 5’-nucleotides but also metabolize it to 2methylamino-6-aminopurine, which is then converted to 5’phosphoribosyl-2-methylamino-6-aminopurine. For methyldiaminopurine synthesis, crude, cell-free extracts of E. coli B require methionine,l ATP, Mg++, and diaminopurine; the methyl carbon of L-methionine is transferred to diaminopurine. The requirements of the system suggested that methionine functions as a precursor for X-adenosylmethionine which supplies the methyl group by transmethylation by the interaction of a specific N-methylpherase. Enzymatic activation of methionine by a Mg++and ATP-dependent conversion to adenosylmethionine has been clearly established by Cantoni (3) as a prerequisite for the transfer of the methyl group of methionine to specific methyl acceptors. The two reactions are as follows: