Thetin–homocysteine transmethylase. The distribution of the enzyme, studied with the aid of trimethylsulphonium chloride as substrate

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Abstract
Evidence is presented that trimethylsulfonium chloride is a substrate for thetin-homocysteine transmethylase, and may be used in the manometric assay of the enzyme. A survey has been made of the distribution of thetin-homocysteine transmethylase in 24 species of plant and animal. The thetin transmethylase activity of the green plants, molds and samples of baker''s yeast studied was negligible. Of the 4 invertebrates examined, only the common shore crab showed possible slight activity. The enzyme was present in appreciable amounts in the liver of all 11 vertebrates tested, and also in small amounts in rat and guinea-pig kidney. It was found to be absent from the spleen, brain and muscle of the rat, mouse and guinea pig.