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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.
This list contains a list of EC numbers for the second group, EC 2, transferases, placed in numerical order as determined by the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology.
The resulting enzyme is thermolabile and in homozygotes, enzymatic activity is depressed to 35% of its usual level. [10] The second variant is a milder one, caused by a homologous 1298C polymorphism. This leads to 68% of the control values of enzyme activity, [ 10 ] and it normally does not lead to low serum folate.
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.
The general mechanism for methyl transfer is a S N 2-like nucleophilic attack where the methionine sulfur serves as the leaving group and the methyl group attached to it acts as the electrophile that transfers the methyl group to the enzyme substrate. SAM is converted to S-Adenosyl homocysteine (SAH) during this process. The breaking of the SAM ...
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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.