Inhibition of rat mast cell protease 1 by vitronectin

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Abstract
Rat mast cell protease 1 (RMCP‐1) is a chymotrypsin‐like serine protease specifically expressed by connective tissue‐type mast cells. The enzyme is stored in the secretary granules in a macromolecular complex with heparin proteoglycan. In the present investigation it was shown that RMCP‐1 is inhibited by vitronectin (VN), an RGD‐containing adhesive glycoprotein with heparin‐binding properties. RMCP‐1 that had been separated from heparin proteoglycan was less susceptible to inhibition than RMCP‐1 present in complex with heparin proteoglycan. Pre‐incubation of VN with purified heparin partially blocked the RMCP‐1 inhibiting activity of VN. Plasma VN had negligible RMCP‐1‐inhibiting activity. However, heat treatment of plasma VN, which is known to expose the heparin‐binding domain, induced RMCP‐1‐inhibiting activity. Affinity chromatography on immobilized VN showed that RMCP‐1 bound with high affinity to VN. The binding of RMCP‐1 to VN was not heparin‐dependent since free RMCP‐1 bound with equal affinity to the immobilized VN as RMCP‐1 present in complex with heparin. The inhibition of RMCP‐1 by VN was shown to be reversible.