Fig. 2.

Connection between the one carbon cycle and the transsulfuration pathway (GSH synthesis). Upper panel The methyl group of methionine is activated by adenylation to form S-Adenosyl-Methionine (SAMe) that acts as the universal methyl donor for any acceptor including DNA: a molecule of homocysteine is formed. Homocysteine can be either re-methylated from folates or betaine or enter the transsulfuration pathway for the synthesis of glutathione (GSH). Lower panel Homocysteine is complexed with serine to form cystathionine and to feed the de-novo synthesis of GSH