Immunological, Physical, and Chemical Evidence for the Identity of Brain and Kidney Post‐Proline Cleaving Enzyme

Abstract: Recent studies from this laboratory have suggested a similarity, if not identity, of thyrotropin releasing factor (TRF) deamidase and post‐proline cleaving enzyme. Bovine brain TRF deamidase was purified to homogeneity and used to elicit antibodies to the enzyme. These antibodies were used to demonstrate identical immunological reactivity between rat brain TRF deamidase and rat kidney post‐proline cleaving enzyme. In addition, both proteins exhibit a molecular weight of 75,000, and have identical K_m values for the synthetic substrate pGlu‐(N‐benzyl‐l‐His)‐Pro‐β‐naphthylamide and identical K₁ values for TRF and luteinizing hormone releasing factor as inhibitors. Finally, the enzymes exhibit the same sensitivities to inhibition by mercury, iodoacetamide, N‐ethylmaleimide, and 5, 5′‐dithiobis‐(2‐nitrobenzoic acid). These results strongly suggest that brain TRF deamidase and kidney postproline cleaving enzyme are identical.