Partial Purification and Characterization of Cystine Lyase from Cabbage (Brassica oleracea var capitata)

Cabbage (Brassica oleracea var capitata) leaves were used as a source of cystine lyase. Diethylaminoethyl-cellulose chromatography resolved two peaks of activity, designated I and II.Cystine lyase I (molecular weight 145,000) and O-acetylserine sulfhydrylase (molecular weight 70,000) were resolved by Bio-Gel A-0.5M chromatography. This isozyme catalyzed an alpha,beta-elimination reaction with cystine, cysteine, O-acetylserine, and several S-substituted cysteines. The substrate specificity was similar to previously reported S-alkylcysteine lyases. The elution profiles during purification, and heat inactivation studies indicated that the above reactions were catalyzed by a single protein. The pH optimun with cystine and cysteine as substrate was 8.5 to 9.0, and the K(m) values were: cystine (0.3 mm), cysteine (0.3 mm), O-acetylserine (6 mm), and S-methylcysteine sulfoxide (1.8 mm).Cystine lyase II was resolved into three peaks (molecular weight greater than 500,000, 240,000, and 145,000) using Bio-Gel A-0.5M chromatography. This enzyme degraded l-cystine, l-cysteine, O-acetylserine, S-methylcysteine sulfoxide, and djenkolic acid. The pH optimum with cystine and cysteine was 8.5 to 9.0, and the K(m) values were: cystine (0.3 mm), cysteine (0.3 mm), O-acetylserine (12.5 mm), and S-methylcysteine sulfoxide (3.7 mm).