Protease inhibitor activity in human skeletal muscle.

Myofibrillar protease activity and activity of inhibitors toward trypsin, chymotrypsin, elastase, and the myofibrillar protease were determined in human skeletal muscle. The protease activity was found to increase in patients with acute and chronic inflammation as well as in patients with metastatic and nonmetastatic tumors. The inhibitory activity directed against trypsin and chymotrypsin was not affected by acute inflammation, while the inhibition of elastase and the myofibrillar protease was increased. Chronic inflammation did not affect the ability of the muscle cytosol to inhibit trypsin and elastase, but increased the inhibition of chymotrypsin and the myofibrillar protease. Nonmetastatic tumors produced an increase in the activity of inhibitors toward trypsin, chymotrypsin, and elastase, while patients bearing metastatic tumors had a high level of cytosolic inhibitors of all the tested proteolytic activities. These results indicate that the myofibrillar protease and the cytosolic protease inhibitors in human skeletal muscle are differentially affected by catabolic conditions.