Partial purification of 2,3-oxidosqualene-lanosterol cyclase from hog-liver. Evidence for a functional thiol residue

2,3-Oxidosqualene-lanosterol cyclase is an intrinsic microsomal protein which can be solubilized by ionic (deoxycholate) and nonionic (emulphogene) detergents with good yields. The hog-liver microsomal cyclase was purified approximately 140-fold by chromatography on DEAE-cellulose and hydroxylapatite. The partially purified enzyme was inactivated by N-ethylmaleimide, following pseudo-first order kinetics, indicating that a cysteine residue is essential for activity.