| Abstract: | Abstract— The administration of the convulsant, l -methionine-dl-sulfoximine (MSO), increased histamine N-methyl transferase (E.C. 2.1.1.8) (HMT) activity in rat and mouse brain and, to a lesser extent, catechol-O-methyl transferase (E.C. 2.1.1.6) (COMT) activity in rat brain. The duration of this effect was shortened by co-administration of l -methionine. The increased HMT activity was seen in 5 or 7 rat brain regions tested. l -Methionine administration had no effect on the activity of either enzyme. Partially purified HMT preparations from rat or guinea-pig brain exhibited no alterations in activity after the in vitro addition of MSO or l -methionine over a wide range of histamine and S-adenosyl-l -methionine concentrations. Rat brain COMT was equally unaffected by MSO and l -methionine. The in vitro inhibition of HMT and COMT by S-adenosyl-l -homocysteine was the same whether tested on preparations derived from MSO-treated or control animals. The data are discussed with respect to the possible involvement of aberrant methylation processes in the MSO-induced seizure. |
