What form of the folate coenzyme is required for the conversion of homocysteine to methionine?
MTHFR catalyzes the reduction of 5,10-methylenetetrahydrofolate (5,10-methylene THF) into 5-methyl tetrahydrofolate (5-MeTHF). The latter is the folate coenzyme required to form methionine from homocysteine (see Figure 2 above).
What is methionine homocysteine cycle?
Homocysteine, a sulfur-containing amino acid, is a metabolite of the essential amino acid methionine, and exists at a critical biochemical intersection in the methionine cycle – between S-adenosylmethionine, the indispensable ubiquitous methyl donor, and vitamins B12 and folic acid.
What is homocysteine broken down into?
What does homocysteine do? When it interacts with the B vitamins, homocysteine converts to two substances: Methionine, an essential amino acid and antioxidant that synthesizes (creates) proteins.
What enzyme synthesizes methionine?
Methionine synthase
The overall reaction transforms 5-methyltetrahydrofolate (N5-MeTHF) into tetrahydrofolate (THF) while transferring a methyl group to Homocysteine to form Methionine. Methionine synthase is the only mammalian enzyme that metabolizes N5-MeTHF to regenerate the active cofactor THF.
How is methionine converted to SAM?
In the mouse, SAM conversion from methionine is limited by saturation of the methionine endogenous pool. SAM is present at a practically unchanged level from the unfertilized oocyte to early morula. SAM synthesis is increased at the time of compaction.
What does the methionine cycle do?
The methionine cycle, via the de novo arm, produces the primary methyl donor AdoMet for the transmethylation of proteins, nucleic acids and other molecules, with far-reaching regulatory roles. Along the route it also yields homocysteine whose own metabolism is at the crossroads of several pathways.
How is homocysteine formed?
Homocysteine (Hcy) is a sulfur containing amino acid formed during the metabolism of methionine (Met) to cysteine (Cys). Hyperhomocysteinemia (HHcy), or increased circulating levels of Hcy, is generally recognized as an independent risk factor for coronary, cerebral, and peripheral atherosclerosis [1–3].
What is folate trap?
It is suggested that in man the methyl folate trap is a normal physiological response to impending methyl group deficiency resulting from a very low supply of methionine. This decreases cellular S-adenosyl-methionine (SAM), which puts at risk important methylation reactions, including those required to maintain myelin.
What is methionine biosynthesis pathway?
The methionine molecule originates from three convergent pathways: the carbon backbone deriving from aspartate, the sulfur atom from cysteine, and the methyl group from the β-carbon of serine (Fig. 99.9) catalyzes the synthesis of cystathionine from cysteine and OPH in a γ-replacement reaction.
What is methionine biosynthesis?
In plants and microorganisms, methionine biosynthesis belongs to the aspartate family, along with threonine and lysine (via diaminopimelate, but not via α-aminoadipate). The main backbone is derived from aspartic acid, while the sulfur may come from cysteine, methanethiol, or hydrogen sulfide.
Does meat increase homocysteine?
Elevated homocysteine levels in the bloodstream have been linked with a wide range of health problems. A high-protein diet, especially one that includes red meat and dairy products, can increase blood levels of homocysteine.
How important is homocysteine for health?
Homocysteine has also been shown to play a crucial role as a key marker for disease development determining longevity and health throughout a person’s life. Women with high homocysteine levels find it harder to conceive, are at risk from repeated early miscarriages and are over twice as likely to experience pregnancy complications.
What is the definition of homocysteine?
Definition of homocysteine. : an amino acid C 4H 9NO 2S that is produced in animal metabolism by the demethylation of methionine and that appears to be associated with an increased risk of cardiovascular disease when occurring at high levels in the blood.