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In the field of enzymology, a betaine-homocysteine S-methyltransferase also known as betaine-homocysteine methyltransferase (BHMT) is a zinc metallo-enzyme that catalyzes the transfer of a methyl group from trimethylglycine and a hydrogen ion from homocysteine to produce dimethylglycine and methionine respectively: [2]
In enzymology, a homocysteine S-methyltransferase (EC 2.1.1.10) is an enzyme that catalyzes the chemical reaction. S-methylmethionine + L-homocysteine 2 L-methionine. Thus, the two substrates of this enzyme are S-methylmethionine and L-homocysteine, and it produces 2 molecules of L-methionine.
In humans it is encoded by the MTR gene (5-methyltetrahydrofolate-homocysteine methyltransferase). [5] [6] Methionine synthase forms part of the S-adenosylmethionine (SAMe) biosynthesis and regeneration cycle, [7] and is the enzyme responsible for linking the cycle to one-carbon metabolism via the folate cycle.
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A second pathway, which is usually restricted to liver and kidney in most mammals, involves betaine-homocysteine methyltransferase (BHMT) and requires trimethylglycine as a cofactor. [ 2 ] DNA processing and epigenetics
S-adenosyl-L-methionine + DNA adenine S-adenosyl-L-homocysteine + DNA 6-methylaminopurine m6A was primarily found in prokaryotes until 2015 when it was also identified in some eukaryotes. m6A methyltransferases methylate the amino group in DNA at C-6 position specifically to prevent the host system to digest own genome through restriction enzymes.
Relevant enzymes include aspartokinase, aspartate-semialdehyde dehydrogenase, homoserine dehydrogenase, homoserine O-transsuccinylase, cystathionine-γ-synthase, Cystathionine-β-lyase (in mammals, this step is performed by homocysteine methyltransferase or betaine—homocysteine S-methyltransferase.)
The enzyme from Escherichia coli consists of two alpha8-beta8 (TIM) barrels positioned face to face and thought to have evolved by gene duplication. [1] The active site lies between the tops of the two barrels, the N-terminal barrel binds 5-methyltetrahydropteroyltri-L-glutamic acid and the C-terminal barrel binds homocysteine.