Which enzyme is responsible for metabolizing homocysteine?

The metabolism of homocysteine primarily involves its conversion into cystathionine, which is facilitated by the enzyme cystathione β-synthase (cystathione synthase). This enzyme catalyzes the reaction between homocysteine and serine to form cystathionine, which is a critical step in the transsulfuration pathway. This metabolic pathway helps in maintaining proper levels of homocysteine in the body, as elevated homocysteine can be a risk factor for cardiovascular diseases.

In contrast, other enzymes mentioned play different roles in related metabolic pathways. For instance, cystathione lyase is responsible for the cleavage of cystathionine into cysteine, alpha-ketobutyrate, and ammonia, which is a subsequent step after the initial conversion of homocysteine into cystathionine. Homocysteine methyltransferase, also known as methionine synthase, is involved in the remethylation of homocysteine to methionine, serving a different purpose in the metabolism of homocysteine. Serine hydroxymethyltransferase performs a separate function in the conversion of serine to glycine and is not directly involved in homocysteine metabolism