title: Betaine:homocysteine methyltransferase--a new assay for the liver enzyme and its absence from human skin fibroblasts and peripheral blood lymphocytes.
abstract: Chronic elevation of plasma homocysteine is associated with increased atherogenesis and thrombosis, and can be lowered by betaine (N,N,N-trimethylglycine) treatment which is thought to stimulate activity of the enzyme betaine:homocysteine methyltransferase. We have developed a new assay for this enzyme, in which the products of the enzyme-catalysed reaction between betaine and homocysteine are oxidised by performic acid before being separated and quantified by amino acid analysis. This assay confirmed that human liver contains abundant betaine:homocysteine methyltransferase (33.4 nmol/h/mg protein at 37 degrees C, pH 7.4). Chicken and lamb livers also contain the enzyme, with respective activities of 50.4 and 6.2 nmol/h/mg protein. However, phytohaemagglutinin-stimulated human peripheral blood lymphocytes and cultured human skin fibroblasts contained no detectable betaine:homocysteine methyltransferase (less than 1.4 nmol/h/mg protein), even after cells were pre-cultured in media designed to stimulate production of the enzyme. The results emphasize the importance of the liver in mediating the lowering of elevated circulating homocysteine by betaine.
authors.affiliation: Department of Cardiovascular Medicine, Prince Henry Hospital, University of New South Wales, Sydney, Australia.
authors.forename: J A
authors.initials: JA
authors.lastname: Wang
authors.forename: N P
authors.initials: NP
authors.lastname: Dudman
authors.forename: J
authors.initials: J
authors.lastname: Lynch
authors.forename: D E
authors.initials: DE
authors.lastname: Wilcken
mesh_terms: D000818:Animals; D001622:Betaine / Q000494:pharmacology; D050940:Betaine-Homocysteine S-Methyltransferase; D002645:Chickens; D005347:Fibroblasts / Q000201:enzymology*; D006710:Homocysteine / Q000097:blood / Q000302:isolation & purification; D006801:Humans; D008099:Liver / Q000201:enzymology*; D008214:Lymphocytes / Q000201:enzymology*; D008715:Methionine / Q000302:isolation & purification; D008780:Methyltransferases / Q000032:analysis* / Q000378:metabolism; D012756:Sheep; D012867:Skin / Q000201:enzymology*
chemical_list: D006710:Homocysteine; D001622:Betaine; D008715:Methionine; D008780:Methyltransferases; C494548:BHMT protein, human; D050940:Betaine-Homocysteine S-Methyltransferase