Densitization of pyruvate carboxylase against acetyl-CoA stimulation by chemical modification

Sheep kidney pyruvate carboxylase has been desensitized against its allosteric effector, acetyl CoA, by limited covalent modification with trinitrobenzene sulphonic acid.Trinitrophenylation of the enzyme resulted in a strong inhibition of the rate of the acetyl CoA-stimulated pyruvate carboxylation and enhancement of the rate of the acetyl CoA-independent reaction. A good correlation was found between the requirement for acetyl CoA of the exchange reactions catalysed by the enzyme and the extent of their inhibition by trinitrobenzene sulphonic acid modification.Spectrophotometric data indicated that one to two lysyl residues per monomer were trinitrophenylated. Modification had only a slight effect on the sedimentation properties of the enzyme.