Immunochemical Studies of Bovine and Frog Liver Glutamate Dehydrogenases

From the ¹ From the Laboratory of Clinical Biochemistry, National Heart Institute, and the Laboratory of Clinical Investigations, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20014

Rabbit antibody prepared against native bovine liver glutamate dehydrogenase is not a competitive inhibitor of coenzyme at active sites or of nucleotides at modifier (allosteric) sites. The antibody, indeed, activates glutamate dehydrogenase at the active sites of both bovine and frog liver enzymes. At modifier sites the antibody is antagonistic to the effects of purine nucleotides. For example, the antibody partially inhibits the activating effects of adenosine diphosphate and the inhibitory effects of guanosine triphosphate on glutamate dehydrogenase activity.

Immunochemical and kinetic experiments indicate that there is a great deal of antigenic similarity between the bovine and frog liver enzymes. These results suggest that the antigenic sites are quite similar in both the bovine and frog enzymes and are not active or allosteric sites. It is possible that antibody is bound to a part of the enzyme molecule which contains neither active nor allosteric sites and which is structurally similar from species to species, while active and allosteric sites differ from species to species.

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