Enzymes involved in the degradation of thyrotropin releasing hormone (TRH) and luteinizing hormone releasing hormone (LH-RH) in bovine brain

Abstract

As part of an investigation of neuropeptide inactivation mechanisms, we have resolved an enzymatic activity in bovine brain which catalyzes the deamidation of thyrotropin releasing hormone (TRH) and the hydrolysis of the Pro9--Gly10--NH2 bond of luteinizing hormone releasing hormone (LH-RH) from a second LH-RH degrading activity which does not degrade TRH. The former activity is similar, if not identical to, the post-proline cleaving enzyme in kidney as it is active toward the post-proline cleaving enzyme substrate CbzGly--Pro--Leu--Gly and inhibited by CbzPro--Phe and diisopropylfluorophosphate. In addition, products derived from the degradation of TRH and LH-RH by this activity show a specific cleavage on the carboxyl side of a proline residue. The latter activity has not yet been characterized with respect to its site of cleavage of the LH-RH molecule due to the presence of other contaminating peptidases.