Inactivation of betaine-homocysteine methyltransferase by adenosylmethionine and adenosylethionine.

Preincubation of betaine-homocysteine methyltransferase, prepared from rat liver, with either S-adenosylmethionine or S-adenosylethionine results in a marked loss of enzyme activity. Gel filtration did not restore activity. However both S-adenosylhomocysteine and L-homocysteine, when added to the preincubation medium, inhibited the inactivation of betaine-homocysteine methyltransferase.