Met is converted into AdoMet by catalytic actions of two isoenzymes, MATI and MATIII, of methionine adenosyl transferase [2, 3].
Figure 2 shows the dynamic logarithmic gains in responses of the metabolite concentrations to an infinitesimal change at t=0 in each independent variable in the methionine cycle at the nominal steady state under the regulation of CBS by AdoMet, i.
After donation of the activated methyl group to an acceptor, AdoMet
is converted into total Hcy by formation of S-adenosyl-L-homocysteine (AdoHcy) (10).
June 1999), reported that "longterm treatment with ADoMet
[SAM] may improve survival or delay liver transplantation in the patients with alcoholic liver cirrhosis, especially in those with less advanced liver disease.
The demethylated product of AdoMet is S-adenosylhomocysteine (AdoHcy), which is hydrolyzed to homocysteine and adenosine in a reversible reaction catalyzed by AdoHcy hydrolase.
Moreover, several studies have shown that AdoHcy is a stronger risk factor for cardiovascular disease than homocysteine (4,7), a finding that makes the determination of AdoMet and AdoHcy an important tool to evaluate the clinical conditions associated with hyperhomocysteinemia.
In terms of synthesis, his group has developed new methods for the preparation of methionine and AdoMet
analogues as well as aminosugars.
In addition, the metabolites, AdoMet
and AdoHcy are responsible for activating and inhibiting many enzymes, which makes the cycle more complex.
/AdoHcy ratio is a more important determinant of cellular methylation potential than the is absolute amount of AdoMet
b) DHFR, dihydrofolate reductase; ND, not determined; AdoHcy, S-adenosylhomocysteine; AdoMet
, S-adenosylmethionine; COMT, catecholamine-O-methyltransferase.
is also the methyl donor in other cellular methyltransferase reactions, including in RNA and protein methylation, synthesis, and detoxification processes.
We have described previously that the methylation of thiopurines leads to depletion of AdoMet