CBS_like: This subgroup includes Cystathionine beta-synthase (CBS) and Cysteine synthase. CBS is a unique heme-containing enzyme that catalyzes a pyridoxal 5'-phosphate (PLP)-dependent condensation of serine and homocysteine to give cystathionine. Deficiency of CBS leads to homocystinuria, an inherited disease of sulfur metabolism characterized by increased levels of the toxic metabolite homocysteine. Cysteine synthase on the other hand catalyzes the last step of cysteine biosynthesis. This subgroup also includes an O-Phosphoserine sulfhydrylase found in hyperthermophilic archaea which produces L-cysteine from sulfide and the more thermostable O-phospho-L-serine.