Nutrition Guide

In enzymology, a homocysteine S-methyltransferase (EC 2.1.1.10) is an enzyme that catalyzes the chemical reaction S-adenosyl-L-methionine + L-homocysteine S-adenosyl-L-homocysteine + L-methionine Thus, the two substrates of this enzyme are S-adenosyl methionine and L-homocysteine, whereas its two products are S-adenosylhomocysteine and L-methionine. This enzyme belongs to the family of transferases, specifically those transferring one-carbon group methyltransferases. The systematic name of this enzyme class is S-adenosyl-L-methionine:L-homocysteine S-methyltransferase. Other names in common use include S-adenosylmethionine homocysteine transmethylase, S-methylmethionine homocysteine transmethylase, adenosylmethionine transmethylase, methylmethionine:homocysteine methyltransferase, adenosylmethionine:homocysteine methyltransferase, homocysteine methylase, homocysteine methyltransferase, homocysteine transmethylase, L-homocysteine S-methyltransferase, S-adenosyl-L-methionine:L-homocysteine methyltransferase, S-adenosylmethionine-homocysteine transmethylase, and S-adenosylmethionine:homocysteine methyltransferase. This enzyme participates in

In enzymology, a thetin-homocysteine S-methyltransferase (EC 2.1.1.3) is an enzyme that catalyzes the chemical reaction dimethylsulfonioacetate + L-homocysteine S-methylthioglycolate + L-methionine Thus, the two substrates of this enzyme are dimethylsulfonioacetic acid and L-homocysteine, whereas its two products are S-methylthioglycolic acid and L-methionine. This enzyme belongs to the family of transferases, specifically those transferring one-carbon group methyltransferases. The systematic name of this enzyme class is dimethylsulfonioacetic acid:L-homocysteine S-methyltransferase. Other names in common use include dimethylthetin-homocysteine methyltransferase, and thetin-homocysteine methylpherase.

In enzymology, a betaine-homocysteine S-methyltransferase (EC 2.1.1.5) is an enzyme that catalyzes the chemical reaction trimethylammonioacetate + L-homocysteine dimethylglycine + L-methionine Thus, the two substrates of this enzyme are trimethylammonioacetate and L-homocysteine, whereas its two products are dimethylglycine and L-methionine. This enzyme belongs to the family of transferases, specifically those transferring one-carbon group methyltransferases. The systematic name of this enzyme class is trimethylammonioacetate:L-homocysteine S-methyltransferase. Other names in common use include betaine-homocysteine methyltransferase, and betaine-homocysteine transmethylase. This enzyme participates in the metabolism of glycine, serine, threonine and also methionine.

Elevated levels of homocysteine have been linked to increased fractures in elderly persons. Elevated levels may be due to renal or liver disease, deficiency of folic acid, vitamin B6 or vitamin B12. The high level of homocysteine will auto-oxidize and react with reactive oxygen intermediates and damage endothelial cells and has a higher risk to form a thrombus. [12][13] Homocysteine does not affect bone density. Instead, it appears that homocysteine affects collagen by interfering with the cross-linking between the collagen fibers and the tissues they reinforce. While the HOPE-2 trial [6] showed a reduction in stroke incidence, in those with

In enzymology, a 5-methyltetrahydropteroyltriglutamate-homocysteine S-methyltransferase (EC 2.1.1.14) is an enzyme that catalyzes the chemical reaction 5-methyltetrahydropteroyltri-L-glutamate + L-homocysteine tetrahydropteroyltri-L-glutamate + L-methionine Thus, the two substrates of this enzyme are 5-methyltetrahydropteroyltri-L-glutamatic acid and L-homocysteine, whereas its two products are tetrahydropteroyltri-L-glutamatic acid and L-methionine. This enzyme belongs to the family of transferases, specifically those transferring one-carbon group methyltransferases. The systematic name of this enzyme class is 5-methyltetrahydropteroyltri-L-glutamate:L-homocysteine S-methyltransferase. Other names in common use include tetrahydropteroyltriglutamate methyltransferase, homocysteine methylase, methyltransferase, tetrahydropteroylglutamate-homocysteine transmethylase, methyltetrahydropteroylpolyglutamate:homocysteine methyltransferase, cobalamin-independent methionine synthase, methionine synthase (cobalamin-independent), and MetE. This enzyme participates in methionine metabolism. It has 2 cofactors: orthophosphate, and zinc.

S-Adenosyl-L-homocysteine is an amino acid derivative used in several metabolic pathways in the organism Escherichia coli. It is an intermediate in the synthesis of cysteine. S-(5'-deoxy-5'-adenosyl)-l-homocysteine is a compound formed by the demethylation of S-adenosyl-L-methionine (SAM).

In enzymology, a S-ribosylhomocysteine lyase (EC 4.4.1.21) is an enzyme that catalyzes the chemical reaction S-(5-deoxy-D-ribos-5-yl)-L-homocysteine L-homocysteine + (4S)-4,5-dihydroxypentan-2,3-dione Hence, this enzyme has one substrate, S-(5-deoxy-D-ribos-5-yl)-L-homocysteine, and two products, L-homocysteine and (4S)-4,5-dihydroxypentan-2,3-dione. This enzyme belongs to the family of lyases, specifically the class of carbon-sulfur lyases. The systematic name of this enzyme class is S-(5-deoxy-D-ribos-5-yl)-L-homocysteine L-homocysteine-lyase [(4S)-4,5-dihydroxypentan-2,3-dione-forming]. Other names in common use include S-ribosylhomocysteinase, and LuxS. This enzyme participates in methionine metabolism.

In enzymology, a homocysteine desulfhydrase (EC 4.4.1.2) is an enzyme that catalyzes the chemical reaction L-homocysteine + H2O hydrogen sulfide + NH3 + 2-oxobutanoate Thus, the two substrates of this enzyme are L-homocysteine and H2O, whereas its 3 products are hydrogen sulfide, NH3, and 2-oxobutanoate. This enzyme belongs to the family of lyases, specifically the class of carbon-sulfur lyases. The systematic name of this enzyme class is L-homocysteine hydrogen-sulfide-lyase (deaminating 2-oxobutanoate-forming). Other names in common use include homocysteine desulfurase, L-homocysteine hydrogen-sulfide-lyase, and (deaminating). This enzyme participates in nitrogen metabolism and sulfur metabolism. It employs one cofactor, pyridoxal phosphate.

In enzymology, a S-adenosylhomocysteine deaminase (EC 3.5.4.28) is an enzyme that catalyzes the chemical reaction S-adenosyl-L-homocysteine + H2O S-inosyl-L-homocysteine + NH3 Thus, the two substrates of this enzyme are S-adenosyl-L-homocysteine and H2O, whereas its two products are S-inosyl-L-homocysteine and NH3. This enzyme belongs to the family of hydrolases, those acting on carbon-nitrogen bonds other than peptide bonds, specifically in cyclic amidines. The systematic name of this enzyme class is S-adenosyl-L-homocysteine aminohydrolase. This enzyme is also called adenosylhomocysteine deaminase.

5-methyltetrahydrofolate-homocysteine methyltransferase, also known as MTR, is a human gene.[1] MTR encodes the enzyme 5-methyltetrahydrofolate-homocysteine methyltransferase. This enzyme, also known as cobalamin-dependent methionine synthase, catalyzes the final step in methionine biosynthesis. Mutations in MTR have been identified as the underlying cause of methylcobalamin deficiency complementation group G.[1] 5-Methyltetrahydrofolate-homocysteine methyltransferase or (MTR) is an enzyme responsible for the production of methionine from homocysteine. MTR forms part of the S-adenosyl methionine cycle and is also called methionine synthase.[2]

Homocysteine is a chemical compound with the formula HSCH2CH2CH(NH2)CO2H. It is a homologue of the naturally-occurring amino acid cysteine, differing in that its side-chain contains an additional methylene (-CH2-) group before the thiol (-SH) group. Alternatively, homocysteine can be derived from methionine by removing the latter's terminal C? methyl group.

In enzymology, an adenosylhomocysteine nucleosidase (EC 3.2.2.9) is an enzyme that catalyzes the chemical reaction S-adenosyl-L-homocysteine + H2O S-(5-deoxy-D-ribos-5-yl)-L-homocysteine + adenine Thus, the two substrates of this enzyme are S-adenosyl-L-homocysteine and H2O, whereas its two products are S-(5-deoxy-D-ribos-5-yl)-L-homocysteine and adenine. This enzyme belongs to the family of hydrolases, specifically those glycosylases that hydrolyse N-glycosyl compounds. The systematic name of this enzyme class is S-adenosyl-L-homocysteine homocysteinylribohydrolase. Other names in common use include S-adenosylhomocysteine hydrolase (ambiguous), S-adenosylhomocysteine nucleosidase, 5'-methyladenosine nucleosidase, S-adenosylhomocysteine/5'-methylthioadenosine nucleosidase, and AdoHcy/MTA nucleosidase. This enzyme participates in methionine metabolism.

Although mammals cannot synthesize methionine, they can still utilize it in a variety of biochemical pathways: Methionine is converted to S-adenosylmethionine (SAM) by (1) methionine adenosyltransferase. SAM serves as a methyl-donor in many (2) methyltransferase reactions and is converted to S-adenosylhomocysteine (SAH). (3) adenosylhomocysteinase converts SAH to homocysteine. There are two fates of homocysteine: Methionine can be regenerated from homocysteine via (4) methionine synthase. It can also be remethylated using glycine betaine (NNN-trimethyl glycine) to methionine via the enzyme Betaine-homocysteine methyltransferase (E.C.2.1.1.5, BHMT). BHMT makes up to 1.5% of all the soluble protein of the liver, and recent evidence suggests that it may

Asymmetric dimethylarginine is created in protein methylation, a common mechanism of post-translational protein modification. This reaction is catalyzed by an enzyme set called S-adenosylmethionine protein N-methyltransferases (protein methylases I and II).[2] The methyl groups transferred to create ADMA are derived from the methyl group donor S-adenosylmethionine, an intermediate in the metabolism of homocysteine. (Homocysteine is an important blood chemical, because it is also a marker of cardiovascular disease). After synthesis, ADMA migrates into the extracellular space and thence into blood plasma. Asymmetric dimethylarginine is measured using high performance liquid chromatography. ADMA concentrations are substantially elevated by native or oxidized LDL cholesterol.[3]

In enzymology, a cystathionine beta-lyase (EC 4.4.1.8) is an enzyme that catalyzes the chemical reaction L-cystathionine + H2O L-homocysteine + NH3 + pyruvate Thus, the two substrates of this enzyme are L-cystathionine and H2O, whereas its 3 products are L-homocysteine, NH3, and pyruvate. This enzyme belongs to the family of lyases, specifically the class of carbon-sulfur lyases. The systematic name of this enzyme class is L-cystathionine L-homocysteine-lyase (deaminating; pyruvate-forming). Other names in common use include beta-cystathionase, cystine lyase, cystathionine L-homocysteine-lyase (deaminating), and L-cystathionine L-homocysteine-lyase (deaminating). This enzyme participates in 5 metabolic pathways: methionine metabolism, cysteine metabolism, selenoamino acid metabolism, nitrogen metabolism, and

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