ENDOPEPTIDASE-24.16B - A NEW VARIANT OF ENDOPEPTIDASE-24.16

A peptidase, isolated from rat testes, is inhibited by 1 mM o-phenanth roline, 1 mu M oxyl-3-phenyl-propyl)-Ala-Ala-Phe-p-aminobenzoate, and 6 mM Pro-ILe, properties similar to those ascribed to endopeptidase 24 .16. The enzyme hydrolyzes dynorphin A-8, neurotensin 1-13, angiotensi n I, and substance P. Kinetic analysis of a series of angiotensin I an alogs showed that substitutions at P-1, P-1', or P-2' had little effec t on K-m or k(cat). Variation of peptide size with a series of dynorph in A peptides showed chain length to be significant. The peptidase cle aved dynorphin A-8 at both Leu(5)-Arg(6) and Arg(6)-Arg(7), and neurot ensin 1-13 at Pro(10)-Tyr(11) and Arg(8)-Arg(9). In contrast, rat endo peptidase 24.16 cleaves dynorphin A-8 at Gly(4)-Leu(5) and Leu(5)-Arg( 6), and neurotensin 1-13 only at Pro(10)-Tyr(11). These findings, as w ell as the observation that endopeptidase 24.16 exhibits a considerabl y higher affinity for Pro-Ile, K-i = 90 mu M, indicates the peptidase isolated in this study is related to, but distinct from, rat endopepti dase 24.16. We propose that this new endopeptidase be referred to as e ndopeptidase 24.16B, while the originally described enzyme be referred to as endopeptidase 24.16A