SUBSTRATE-SPECIFICITY DIFFERENCES BETWEEN RECOMBINANT RAT TESTES ENDOPEPTIDASE EC-3.4.24.15 AND THE NATIVE BRAIN ENZYME

We have characterized and compared the substrate specificity of affini ty-purified recombinant rat testes endopeptidase EC 3.4.24.15 (EP 24.1 5) with that reported for the isolated brain enzyme. Of the peptides t ested, only bradykinin, dynorphin A(1-8), and neurotensin were efficie ntly cleaved by the recombinant enzyme (k(cat)/K-m = 3.0, 2.8 and 0.5 x 10(5) M-(1)sec(-1), respectively); other peptides considered substra tes of EP 24.15 (gonadotropin-releasing hormone, substance P, somatost atin and angiotensin) were not metabolized. The enzyme was inhibited b y metal ion chelators and thiol-reactive agents, as well as a specific EP 24.15 inhibitor boxy-3-phenylpropyl]-Ala-Ala-Tyr-p-aminobenzoate), thus confirming the enzyme as a thiol-dependent metalloendopeptidase. The observed discrepancies in substrate specificity of the recombinan t testicular and the isolated brain enzymes may result from tissue-spe cific forms and/or post-translational modifications of EP 24.15. (C) 1 995 Acadamic Press, Inc.