The Purification and Subunit Structure of Cysteine Desulfhydrase from Salmonella typhimurium

The inducible enzyme, cysteine desulfhydrase, was purified from Salmonella typhimurium to a state of near homogeneity. This enzyme has a very low tryptophanase activity, lacks cystathionase and tryptophan synthetase activities, and appears to be a specific cysteine desulfhydrase. The purified native enzyme has an s20,w of 10.4 and a molecular weight of 229,000 as determined by equilibrium sedimentation. Polyacrylamide electrophoresis in sodium dodecyl sulfate showed a single species of polypeptide chain with a molecular weight of 37,000 while the pyridoxal phosphate content was found to be 1 mole per 37,700 g of protein. These data, together with the results of amino acid analyses, tryptic peptide maps, and an NH2-terminal amino acid analysis, indicate that the native enzyme is a hexamer, containing 6 moles of pyridoxal phosphate, and composed of six identical polypeptide chains with NH2-terminal serines.