Genetic Variation of Homocysteine Metabolism and Atherosclerosis

摘要

Homocysteine is an amino acid that is found in mammalian cells and in the plasma. It arises in the first instance from the catabolism of the essential dietary amino acid methionine, to which it is very similar in structure (Fig. 1). This process takes place mainly in the liver as a constituent of the so-called methylation cycle (Fig. 2).Examination of the structures of methionine and homocysteine show them to be identical except for a conversion that has resulted in the removal of a methyl group (-CH3) from the former (I). In vivo, this transfer of the methyl group of methionine has important consequences (2). In all cells, there are dozens of enzymes called methyltransferases. As the name suggests, these are involved in the donation (or transfer) of a methyl group from the activated form of methionine, s-adenosylme-thionine (SAM). The products of such methyltransferase reactions are always s-adenosylhomocysteine (SAH) and the methylated version of the substrate for the reaction (3).