4-Hydroxy-2-ketoglutarate Aldolase of Rat Liver

Abstract 4-Hydroxy-2-ketoglutarate aldolase of rat liver has been purified to near homogeneity. Binding studies, in which glyoxylate or pyruvate is covalently linked to the enzyme by reduction with sodium borohydride, suggest that 1 or 2 moles of each substrate are bound per mole of enzyme inactivated. With the use of minimum effective borohydride, enzyme inactivation requires lower concentrations of pyruvate than of glyoxylate. Pyruvate and glyoxylate appear to exclude each other in direct measurements of binding. In kinetic studies, high ratios of glyoxylate to pyruvate are inhibitory to the condensation reaction and there is a less clear suggestion of pyruvate inhibition competitive with glyoxylate. All of these findings suggest that glyoxylate and pyruvate may be bound by the same lysine residue or residues. There is also nonspecific inhibition by monovalent salts of the condensation reaction, but not of the cleavage reaction. Both glyoxylate and pyruvate tend to reduce the magnitude of inhibition by salt.