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

With raised levels of ADMA seemingly to be associated with adverse human health consequences for cardiovascular disease, metabolic diseases and also a wide range of diseases of the elderly, the possible lowering of ADMA levels may have important therapeutic effects. However it has yet to be established whether ADMA levels can be manipulated and, more importantly, if this results in useful clinical benefits. The association of ADMA with abnormalities of lipid regulation suggested that supplements of free fatty acids might manipulate ADMA levels. However research has failed to show that these have an effect.[4][5] ADMA role has been linked with elevated levels

As a consequence of the biochemical reactions in which homocysteine is involved, deficiencies of the vitamins folic acid (B9), pyridoxine (B6), or B12 (cyanocobalamin) can lead to high homocysteine levels.[2] Supplementation with pyridoxine, folic acid, B12 or trimethylglycine (betaine) reduces the concentration of homocysteine in the bloodstream.[3] [4] Increased levels of homocysteine are linked to high concentrations of endothelial asymmetric dimethylarginine. Recent research suggests that intense, long duration exercise raises plasma homocysteine levels, perhaps by increasing the load on methionine metabolism.[5] Elevations of homocysteine also occur in the rare hereditary disease homocystinuria and in the methylene-tetrahydrofolate-reductase polymorphism genetic traits. The latter

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]

Adequate concentrations of folate, vitamin B12, or vitamin B6 may decrease the circulating level of homocysteine, an amino acid normally found in blood. There is evidence that an elevated homocysteine level is an independent risk factor for heart disease and stroke.[24] The evidence suggests that high levels of homocysteine may damage coronary arteries or make it easier for blood clotting cells called platelets to clump together and form a clot.[25] However, there is currently no evidence available to suggest that lowering homocysteine with vitamins will reduce risk of heart disease. Clinical intervention trials are needed to determine whether supplementation with

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.

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.

There has been much concern about the possibility of increased risk for heart attack and stroke in users of NSAID drugs, particularly COX-2 selective NSAIDs such as celecoxib, since the withdrawal of the COX-2 inhibitor rofecoxib (Vioxx) in 2004. Like all NSAIDs on the U.S. market, celecoxib carries an FDA-mandated "black box warning" for cardiovascular and gastrointestinal risk. In February 2007, the American Heart Association warned that celecoxib should be used "as a last resort on patients who have heart disease or a risk of developing it", and suggested that paracetamol (acetaminophen), or certain older NSAIDs, such as naproxen, may

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.

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