Their findings indicate that one of the enzymes, methionine synthase
, together with cystathionine synthase and 5, 10-methylene tetrahydrofolate reductase, responsible for homocysteine metabolism, is likely to be abnormal in affected pregnancies.
Two enzymes are involved in this pathway, methylmalonyl-CoA mutase and methionine synthase
. Adenosylcobalamin (AdoCbl) and methylcobalamin (MeCbl) are cofactors for these 2 enzymes.
These are methylenetetrahydrofolate reductase (MTHFR), methionine synthase
(MTR), and methionine synthase
Cobalamin is an essential water soluble vitamin  required as a coenzyme for methionine synthase
and methylmalonyl-CoA mutase , in the methylation of DNA and the Krebs cycle, respectively.
In line with these observations, an NADPH-dependent diflavin enzyme, methionine synthase
reductase, has been shown to reduce the CBS heme in vitro in the presence of CO or nitrite, generating, respectively, the ferrous-CO or ferrous-NO CBS adducts [18, 67, 68].
Barbaux et al., "The methionine synthase
reductase (MTRR) A66G polymorphism is a novel genetic determinant of plasma homocysteine concentrations," Atherosclerosis, vol.
Vitamin [B.sub.12] is a required cofactor for methionine synthase
, while folic acid is a required cofactor for 5, 10-methylenetetrahydrofolate reductase.
The metabolism of the amino acid homocysteine consists of a vitamin B6-dependent trans-sulfuration pathway involving the enzyme Cystathionine [beta]-Synthase (CBS) and a folate- and vitamin B12-dependent remethylation pathway involving the enzymes Methylene Tetrahydrofolate Reductase (MTHFR) and methionine synthase
This material causes defection of methionine synthase
that converts homocysteine to methionine and there for decreases concentration of homocysteine .
(6) During this period, cobalamin-dependent enzymes, namely methionine synthase
are inhibited, the ability of the cells to produce methionine from homocysteine is impaired, and consequently plasma homocysteine level increases.
(MTR), methionine synthase
reductase (MTRR), transcobalamin 2 (TC2), cystathionine beta synthase (CBS), and methylenetetrahydrofolate dehydrogenase (MTHFD1) are very important enzymes involved in folate/homocysteine (Hcy) metabolism and play essential roles in synthesis and repair of DNA and methylation reactions .
The group of metabolism-related proteins  included the alteration of methionine synthase
(spots 6, 7), S-adenosylmethionine synthase (spot 16), and P-(S)-hydroxymandelonitrile lyase (spot 29).