The protein encoded by this gene acts as a homotetramer to catalyze the conversion of homocysteine to cystathionine, the first step in the transsulfuration pathway. The encoded protein is allosterically activated by adenosyl-methionine and uses pyridoxal phosphate as a cofactor.

Defects in this gene can cause cystathionine beta-synthase deficiency (CBSD), which can lead to homocystinuria. Multiple alternatively spliced transcript variants have been found for this gene. [provided by RefSeq, May 2010]