Procollagen Processing. Limited Proteolysis of COOH-Terminal Extension Peptides by a Cathepsin-Like Protease Secreted by Tendon Fibroblasts

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Abstract
An enzymatic activity, capable of removing the COOH-terminal extensions of type I chick procollagen was demonstrated in embryonic chick tendons and in cultured tendon fibroblasts utilizing 2 new methods of analysis. The protease was purified by a combination of ultrafiltration, concanavalin A affinity chromatography and gel filtration. The isolated protein has an apparent Mr [MW] of 43,000 by gel filtration and sodium dodecyl sulfate gel electrophoresis. The enzyme shows a major pH optimum at 4.2 and is susceptible to inhibitors such as pepstatin and leupeptin; it seems related to the cathepsins. The possibility that this enzyme plays a role in the limited proteolytic processing of procollagen is discussed.