CHARACTERIZATION OF A MITOCHONDRIAL METALLOPEPTIDASE REVEALS NEUROLYSIN AS A HOMOLOG OF THIMET OLIGOPEPTIDASE

We have isolated a metallopeptidase from rat liver, The peptidase is p rimarily located in the mitochondrial intermembrane space, where it in teracts non-covalently with the inner membrane, The enzyme hydrolyzes oligopeptides, the largest substrate molecule found being dynorphin A( 1-17); it has no action on proteins, and does not interact with alpha( 2)-macroglobulin, and can therefore be classified as an oligopeptidase , We term the enzyme oligopeptidase M, Oligopeptidase M acts similarly to thimet oligopeptidase (EC 3.4.24.15) on bradykinin and several oth er peptides, but hydrolyzes neurotensin exclusively at the -Pro+Tyr- b ond (the symbol + is used to indicate a scissile peptide bond) rather than the -Arg+Arg- bond. The enzyme is inhibited by chelating agents a nd some thiol-blocking compounds, but differs from thimet oligopeptida se in not being activated by thiol compounds, The peptidase is inhibit ed by Pro-Ile, unlike thimet oligopeptidase, and the two enzymes are s eparable in chromatography on hydroxyapatite, The N-terminal amino aci d sequence of rat mitochondrial oligopeptidase M contains 19 out of 20 residues identical with a segment of rabbit microsomal endopeptidase and 17 matching the corresponding segment of pig-soluble angiotensin I I-binding protein, Moreover, the rat protein is recognized by a monocl onal antibody against rabbit soluble angiotensin II-binding protein, a ll of which is consistent with these proteins being species variants o f a single protein that is a homologue of thimet oligopeptidase, The b iochemical properties of the mitochondrial oligopeptidase leave us in no doubt that it is neurolysin (EC 3.4.24.16), for which no sequence h as previously been reported, and which has not been thought to be mito chondrial.