Characterization of the enzymic capacity for cysteine desulphhydration in liver and kidney of the rat

Abstract

The contribution of cystathionine .gamma.-lyase [EC 4.4.1.1, CTL], cystathionine .beta.-synthase [EC 4.2.1.22, CTS] and cysteine aminotransferase [EC 2.6.1.3, CAT] coupled to 3-mercaptopyruvate sulfurtransferase [EC 2.8.1.2, MPST] to cysteine desulfhydration in rat liver and kidney was assessed with 4 different assay systems. CTL and CTS were active when homogenates were incubated with 280 mM L-cysteine and 3 mM pyridoxal 5''-phosphate at pH 7.8. CAT in combination with MPST catalyzed essentially all of the H2S production from cysteine at pH 9.7 with 160 mM cysteine, 2 mM pyridoxal 5''-phosphate, 3 mM 2-oxoglutarate and 3 mM dithiothreitol. At more physiological concentrations of cysteine (2 mM) CTL and CTS both appeared to be active in cysteine desulfhydration, whereas the aminotransferase pathway did not. The effect of inhibition of CTL by a suicide inactivator, propargylglycine, in the intact rat was also investigated; there was no significant effect of propargylglycine administration on the urinary excretion of total 35S, 35SO42- or [35S]taurine formed from labeled dietary cysteine.