Inhibition of transmethylations of biogenic amines by S-adenosylhomocysteine. Enhancement of transmethylation by adenosylhomocysteinase.

The supernatant fraction of brain homogenate stimulates partially pursed phenylethanolamine N-methyltransferase, catechol methyltransferase, and acetylserotonin methyltransferase activities in uifro. The stimulating factor was purified, and the mechanism of stimulation was investigated. The results show that S-adenosylhomocysteine, a product from S-adenosyhnethionine, is a potent inhibitor of these methyltransferases, and that the stimulating factor in brain is an enzyme which enhances transmethylations by hydrolyzing S-adenosylhomocysteine. The question is raised whether inhibition by S-adenosylhomocysteine or removal of inhibition by adenosylhomocysteinase might control transmethylations of biogenic amines.