Biosynthesis of Methionine in Saccharomyces Cerevisiae. Kinetics and Mechanism of Reaction of S-adenosylmethionine:homocysteine Methyltransferase.

It is now firmly established that X-adenosylmethionine is the most important biological methyl donor in a variety of transmethylation reactions (I). However, in spite of the large number of methyltransferases that have been described, little information is available concerning the enzymatic mechanism of the methyl transfer from S-adenosylmethionine to a substrate resulting in the formation of a methylated product and X-adenosylhomocysteine. In previous work (2) we have described a methyltransferase obtained from Xaccharomyces cerevisiae that catalyzes the following reaction