| Abstract: | Cysteine conjugate β-lyases convert S-substituted cysteine conjugates to pyruvate, ammonia, and thiols. A simple assay for cysteine conjugate β-lyase activity was developed with S-(2-benzothiazolyl)cysteine as the substrate. The production of 2-mercaptobenzothiazole was measured by its intense absorbance at 321 nm in trichloroacetic acid-quenched reaction mixtures. The formation of 2-mercaptobenzothiazole was directly proportional to protein concentrations of 0.17 to 1.2 mg/ml with rat liver cytosol as the source of β-lyase activity. Production of 2-mercaptobenzothiazole was stoichiometric with pyruvate and was increased by addition of pyridoxal phosphate only at reaction times of 5 min or longer. The simplicity, sensitivity, and specificity of this procedure offer significant advantages over other methods for the assay of cysteine conjugate β-lyase activity. |
