The synthesis of methionine by enzymic transmethylation: VII. Existence of two separate homocysteine methylpherases on mammalian liver

Abstract

In addition to the enzyme thetin-homocysteine methylpherase, rat and horse livers contain a second enzyme capable of catalyzing the methylation of homocysteine to form methionine. This enzyme differs from thetin-homocysteine methylpherase (a) in its substrate specificity which is much more favorable to the naturally occurring methyl donor betaine; (b) in its behavior towards calcium phosphate and alumina gels, and Sephadex G-75; (c) in its intracellular distribution; and (d) in its concentration in neonatal and regenerating rat liver. The physiological significance of the two homocysteine methylpherases is discussed.