Biochemical and genetic characterization of mammalian methionine synthase

Mammalian methionine synthase (5-methyl-homocysteine methyltransferase; EC 2.1.1.13) is a cobalamin dependent enzyme that catalyzes the transfer of a methyl group from methyltetrahydrofolate to homocysteine, and generates methionine and tetrahydrofolate. Methionine synthase activity, in two classes of patients with defects in cobalamin metabolism, cblG and cblE, is compromised. These patients exhibit severe megaloblastic anemia, homocystinuria, homocysteinaemia and hypomethionaemia. Hyperhomocysteinaemia is a risk factor for cardiovascular disease. High levels of homocysteine have also been linked to neural tube defects. In the present study, a combination of biochemical analyses and molecular genetic approaches have been used to identify culpable loci in patients belonging to the two complementation groups, cblE and cblG. Also, preliminary studies on the regulation of methionine synthase activity by B$\sb{12}$ have been conducted