Alkaline proteolytic activity from smooth muscle of mouse small intestine

An alkaline proteolytic activity from the smooth muscle of mouse small intestine has been separated and characterised. The activity sedimented after high-speed centrifugation, but was released into the soluble phase after treatment with 2.0 M KCl. The proteinase was found to be sensitive to salt concentration and the activity was maximal between 0.1-0.5 M NaCl/KCl and pH 9.5. This activity was completely inhibited by di-isopropylphosphoro fluoridate suggesting that it is a serine endopeptidase. The proteinase was identified as chymotrypsin-like due to the inhibition observed with the agents chymostatin, lima bean and soya bean trypsin inhibitor. These characteristics of the alkaline proteinase resemble the properties of the mast cell enzyme, chymase. The enzyme activity was measured in 48/80 treated animals and the mutant strain w/wv, which do not contain mast cells. No significant reduction in the enzyme activity was observed.