Characteristics of the enzymatic capacity for cysteine desulfhydration in cat tissues

Abstract

1. 1. When H 2S production from cysteine was assayed in systems that contained 2 mM l-cysteine, 0.1 mM pyridoxal 5′-phosphate, 0.4 mM α-ketoglutarate, 150 mM potassium phosphate, pH 7.4, and liver or kidney homogenates, cysteine desulfhydration appeared to be catalyzed by both cystathionine γ-lyase and the coupled activity of cysteine aminotransferase and 3-mercaptopyruvate sulfurtransferase. The contribution of cystathionine β-synthase could not be assessed from our data. 2. 2. When maximal rates of cysteine desulfhydration were measured in the presence of saturating concentrations of cysteine, α-ketoglutarate, and pyridoxal phosphate at pH 9.6, activity was highest in liver and heart. When α-ketoglutarate was omitted and the pH was 7.6, activity was highest in liver and kidney.