An immunoadsorbent column chromatography procedure utilizing antibody to one component of a multienzyme complex has been utilized for purification of the second component of this complex. Rabbit immunoglobulin G (IgG) specific for the O-acetylserine sulfhydrylase component of the multienzyme complex cysteine synthetase was linked to Sepharose 4B resin. A crude preparation of cysteine synthetase was bound to a column of IgG-Sepharose, other proteins were removed by washing, and the serine acetyltransferase component of the complex was eluted with 50 mM O-acetylserine, which dissociates the complex of the two enzymes. This purification step produces about a 4OO-fold increase in specific activity. The terminal reactions in the synthesis of cysteine in plants and bacteria are: L-set-me + acetyl CoA' * U-acetyl-L-serine + CoA, [l] 0-acetyk-serine + S-+ L-cysteine + acetate. [2] 1 Abbreviations used: CoA, coenzyme A: IgG, immunoglobulin G; PBS, phosphate-buffered saline: OASS, O-acetylserine sulfhydrylase; SDS, sodium dodecyl sulfate.
* To avoid confusion between the mandated name for this enzyme, cysteine synthase, and the trivial name for the complex, cysteine synthetase, we will refer to it by its original name, O-acetylserine sulfhydrylase.