Search results
Results from the WOW.Com Content Network
In the body, homocysteine can be recycled into methionine or converted into cysteine with the aid of vitamin B 6, B 9, and B 12. [3] High levels of homocysteine in the blood (hyperhomocysteinemia) is regarded as a marker of cardiovascular disease, likely working through atherogenesis, which can result in ischemic injury.
Homocysteine (left) and methionine (right) are related by demethylation and remethylation. Remethylation is a major step in the conversion of homocysteine to the essential amino acid methionine . The remethylation process involves the enzyme methionine synthase (MS), which requires vitamin B 12 as a cofactor, and also depends indirectly on ...
Methionine synthase catalyzes the final step in the regeneration of methionine (Met) from homocysteine (Hcy). Both the cobalamin-dependent and cobalamin-independent forms of the enzyme carry out the same overall chemical reaction, the transfer of a methyl group from 5-methyltetrahydrofolate (N 5 -MeTHF) to homocysteine, yielding ...
The production of homocysteine through transsulfuration allows the conversion of this intermediate to methionine, through a methylation reaction carried out by methionine synthase. The reverse pathway is present in several organisms, including humans, and involves the transfer of the thiol group from homocysteine to cysteine via a similar ...
This is hydrolysed to homocysteine and adenosine by S-adenosylhomocysteine hydrolase EC 3.3.1.1 and the homocysteine recycled back to methionine through transfer of a methyl group from 5-methyltetrahydrofolate, by one of the two classes of methionine synthases (i.e. cobalamin-dependent (EC 2.1.1.13) or cobalamin-independent (EC 2.1.1.14)).
Elevated homocysteine is an independent risk factor for cardiovascular disease and inversely correlated to consumed vitamin B12/B6 and folate levels. [37] Homocysteine methylation to methionine is catalyzed by MTR, resulting in appropriate intracellular levels of methionine and tetrahydrofolate, alongside non-toxic homocysteine levels.
Homocysteine is a non-protein amino acid, synthesized from methionine and either recycled back into methionine or converted into cysteine with the aid of the B-group vitamins [citation needed]. About 50% of homocysteine [citation needed] is converted back to methionine by remethylation via the methionine synthase major pathway.
The methionine that is not converted into protein is converted to S-adenosyl-methionine which goes on to form homocysteine again. Betaine is, therefore, only effective if the quantity of methionine to be removed is small. Hence treatment includes both betaine and a diet low in methionine.