Abstract
The methylation of homocysteine by dimethylthetin in the presence of rat-liver suspensions was studied by estimation of the methionine formed. The estimation of methionine under the particular experi-mental conditions employed is discussed. A manometric method for following the course of the transmethylation, based on the formation of acid in the reaction, is described. The enzyme involved, thetin-homo-cysteine transmethylase, was partially purified from rat liver by am-monium sulfate fractionation and some of its properties were investi-gated.