Purification and characterization of cysteine synthetase, a bifunctional protein complex, from Salmonella typhimurium.

Cysteine synthetase in Salmonella typhimurium is a multifunctional protein complex of molecular weight 309,000 which catalyzes the two-step synthesis of L-cysteine from L-serine, acetyl-CoA, and sulfide. Certain enzymic and chemical properties of a purified preparation of cysteine synthetase have been studied. 0-Acetyl-L-serine at a concentration of lop4 to 10m3 IVI causes this complex to dissociate reversibly into 1 molecule of serine transacetylase (mol wt 160,000) and 2 molecules of 0-acetylserine sulfhydrylase (mol wt 68,000). Serine transacetylase and O-acetylserine sulfhydrylase have been resolved from one another by Sephadex gel filtration in the presence of Oacetyl-L-serine. The 0-acetylserine sulfhydrylase associated with serine transacetylase in the complex appears to be identical with the previously described free O-acetylserine sulfhydrylase.