The activities of 'Pz-peptidase' and 'endopeptidase 24.15' are due to a single enzyme.

It was found that Pz-peptidase (assayed with 2,4-dinitrophenyl-Pro-Leu-Gly-Pro-Trp-D-Lys) and endopeptidase 24.15 (assayed with benzoyl-Gly-Ala-Ala-Phe-p-aminobenzoate) were co-purified from rat skeletal muscle, were co-eluted in high-resolution gel chromatography and co-existed in a homogeneous preparation of rat testis endopeptidase 24.15. The action of partially purified Pz-peptidase from rat testis on 4-phenylazobenzyloxycarbonyl-Pro-Leu-Gly-Pro-D-Arg was blocked by an inhibitor of endopeptidase 24.15, and also by a substrate of this enzyme. The partially purified enzyme hydrolysed two substrates of endopeptidase 24.15 with Km values similar to those published previously, and its action on 2,4-dinitrophenyl-Pro-Leu-Gly-Pro-Trp-D-Lys was inhibited by compounds that are considered specific for endopeptidase 24.15. We conclude that the activities previously attributed to two distinct enzymes are due to only one, and that the merging of the two literatures may lead to new lines of research.