Cystathionine beta-synthase (CBS) is a crucial enzyme in the trans-sulfuration pathway that catalyzes the conversion of homocysteine to cystathionine, which is subsequently converted to cysteine. It is a pyridoxal 5鈥?phosphate (PLP)-dependent enzyme with a modular three-domain structure. The N-terminal domain binds a heme cofactor that acts as a redox sensor, while the C-terminal domain contains a tandem CBS domain that binds S-adenosylmethionine (SAM), an allosteric activator. Mutations in the CBS gene can lead to homocystinuria, a condition associated with cardiovascular, ocular, skeletal, and central nervous system complications. CBS is also involved in hydrogen sulfide (H鈧係) production, an important gasotransmitter with various physiological functions.