CHAPTER 7: Betaine-Homocysteine S-Methyltransferase
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Published:15 May 2015
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T. A. Garrow, in Betaine: Chemistry, Analysis, Function and Effects, ed. V. R. Preedy, The Royal Society of Chemistry, 2015, pp. 90-101.
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Betaine-homocysteine S-methyltransferase (BHMT: EC 2.1.1.5) catalyzes a methyl transfer from glycine betaine (or betaine, Bet) to homocysteine (Hcy) to form dimethylglycine (DMG) and methionine (Met). The reaction mechanism is ordered bi bi: Hcy is the first substrate to bind, and Met is the last product off. Bet is an intermediate of choline oxidation, and BHMT is the only enzyme in mammals known to use Bet as a substrate. BHMT is an important determinant of plasma Hcy concentration, and as such, the regulation of BHMT expression and any genetic variation that affects BHMT expression or function is germane to pathologies associated with hyperhomocysteinemia, which include vascular diseases, thrombosis and some cognitive disorders of aging. This chapter summarizes current knowledge regarding BHMT structure and function.