Thetin–homocysteine transmethylase. Some further characteristics of the enzyme from rat liver

The Biochemistry of Sulfonium Compounds

“…The thetin-homocysteine transmethylase of liver has been partially purified in several laboratories. Maw has developed a manometric method for following the course of the transmethylation (101) and has partially purified the enzyme from rat liver (102). In addition, he has shown that this enzyme is widely distributed among vertebrates (102a).…”

“…111 both cases L-homocysteine is the only methyl acceptor known. Dimethylacetothetin is the best methyl donor, but ethylmethylacetothetin and dimethyl-P-propiothetin are also active, and Maw (102) states that dimethyl-7-butyrothetin shows one-fourth the activity of acetothetin. Durell et al report that S-methylmethionine is utilized at a rate of 0.003 times that of dimethylacetothetin, whereas Maw finds Smethylmethionine to be one-fourth as active as dimethylacetothetin.…”

“…Extracts of a variety of bacteria and yeasts as well as rat liver (102,109,110) are good sources of the enzyme. The reaction is stereospecific in that only L-homocysteine and S-methyl-L-methionine are suitable as substrates.…”