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

TLDR

The study evaluated the contributions of cystathionine γ‑lyase, cystathionine β‑synthase, and the cysteine aminotransferase/3‑mercaptopyruvate sulphurtransferase pathway to cysteine desulphhydration in rat liver and kidney using four distinct assay systems. Four assay systems were employed, and the effect of cystathionine γ‑lyase inhibition by the suicide inactivator propargylglycine on urinary excretion of labeled sulfur species was also examined in intact rats. Cystathionine γ‑lyase and β‑synthase were active at high cysteine concentrations, whereas the aminotransferase pathway dominated H₂S production at pH 9.7; at physiological cysteine (2 mM) only the γ‑lyase and β‑synthase pathways were active, and propargylglycine inhibition had no significant effect on urinary excretion of ³⁵S, ³⁵SO₄²⁻ or ³⁵S‑taur.

Abstract

The contribution of cystathionine gamma-lyase, cystathionine beta-synthase and cysteine aminotransferase coupled to 3-mercaptopyruvate sulphurtransferase to cysteine desulphhydration in rat liver and kidney was assessed with four different assay systems. Cystathionine gamma-lyase and cystathionine beta-synthase were active when homogenates were incubated with 280 mM-L-cysteine and 3 mM-pyridoxal 5′-phosphate at pH 7.8. Cysteine aminotransferase in combination with 3-mercaptopyruvate sulphurtransferase catalysed essentially all of the H2S production from cysteine at pH 9.7 with 160 mM-L-cysteine, 2 mM-pyridoxal 5′-phosphate, 3 mM-2-oxoglutarate and 3 mM-dithiothreitol. At more-physiological concentrations of cysteine (2 mM) cystathionine gamma-lyase and cystathionine beta-synthase both appeared to be active in cysteine desulphhydration, whereas the aminotransferase pathway did not. The effect of inhibition of cystathionine gamma-lyase 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, 35SO4(2-) or [35S]taurine formed from labelled dietary cysteine.