Proline endopeptidase was purified from human muscle by anion-exchange chromatography, thiol-affinity chromatography and chromatography on hydroxyapatite. The enzyme gave a single band on polyacrylamide gel electrophoresis. Activity was maximum at pH 7.0-7.5. The molecular weight (by gel filtration) was 69,000. The enzyme hydrolysed benzyloxycarbonyl-Gly-Pro-7-amido-4-methylcoumarin with Km 32 microM. It was inhibited by di-isopropyl phosphofluoridate and 4-hydroxymercuriphenyl sulphate. Bacitracin inhibited at higher concentrations but lower concentrations stimulated the activity. The enzyme activity appeared largely in the soluble fraction following fractionation of rat muscles. Proline endopeptidase activity in rat muscle was unaltered by treatment of the animals with compound 48/80, a mast cell degranulator.
        
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Daly DJ, Maskrey P, Pennington RJ (1985) Characterization of proline endopeptidase from skeletal muscle International Journal of Biochemistry17: 521-4
Daly DJ, Maskrey P, Pennington RJ (1985) International Journal of Biochemistry17: 521-4