Comparative inhibitory effects of vitamins on methylating enzymes

Abstract

1. 1. The effects of naturally occurring vitamins on two important methylating enzymes, 2. histamine N-methyltransferase and catechol O-methyltransferase, were investigated. It was found that, of all the vitamins tested in vitro, vitamin B 6 (pyridoxal-5′-phosphate) was the most potent inhibitor of both enzymes. 3. 2. Vitamin B 6 inhibited both enzymes competitively with respect to their substrates (histamine or norepinephrine) and non-competitively with respect to S-adenosylmethionine. 4. 3. The inhibition of catechol O-methyltransferase by vitamin B 6 was complex and dependent on magnesium ion concentration. Maximum inhibition was observed when the metal ion concentration was equal to 10 -3 M. © 1972.