The identification of the major excreted protein (MEP) from a transformed mouse fibroblast cell line as a catalytically active precursor form of cathepsin L.

摘要: The major excreted protein (MEP) purified from Kirsten-virus-transformed 3T3 fibroblasts and mature human cathepsin L were compared in respect to a number of catalytic criteria found be similar. Mr MEP is 39,000, whereas that 30,000. Sequence data suggested could pro-form mouse L. Both enzymes acted on the synthetic substrate benzyloxycarbonyl-Phe-Arg-7-(4-methyl)coumarylamide with similar constants optimally at pH 5.5. rapidly inactivated by active-site-directed inhibitors benzyloxycarbonyl-Phe-Phe-diazomethane L-3-carboxy-trans-2,3-epoxypropionyl-leucylamido-(4-guanidin o)butane, furthermore, 3H-labelled L-3-carboxy-trans-2,3-epoxypropionyl-leucylamido-(4-acetamid which binds covalently heavy chain L, also bound MEP. autolyses 3.0 give lower-Mr (35,000 30,000) forms, but all forms react radiolabelled inhibitor. No autolysis occurred above 5.0. hydrolysed azocasein 5.0, demonstrating it capable hydrolysing substrates without autolytic activation. Unlike stable, not active, neutral pH. present work shows can secreted as higher-Mr precursor stable extracellular fluids only active where local values fall below 6.0. These results suggest extra N-terminal peptide an activation peptide, regulatory affecting pH-stability activity