FIGURE 1.
CBS and the trans-sulfuration pathway of the methionine cycle. CBS catalyzes the condensation of homocysteine (Hcy) with cysteine (Cys) or serine (Ser) forming cystathionine (Cysth) and either H2S or H2O. CBS can also catalyze the conversion of Cys into Ser or lanthionine (Lanth) with concomitant production of H2S. CBS is allosterically activated by AdoMet and inhibited by NO• and CO. Met, methionine; MAT, methionine adenosyltransferase; MT, methyltransferases (involved in methylation reactions); SAHH, S-adenosyl-l-homocysteine hydrolase; CGL, cystathionine γ-lyase; GSH, glutathione.