Protease inhibitor activity in rat skeletal muscle.

The cytosol fraction obtained by homogenization of rat gastrocnemius muscle inhibited the activities of rat alkaline myofibrillar protease, bovine trypsin and bovine chymotrypsin. The inhibition of the three proteolytic enzymes by muscle cytosol changed differentially during ageing, fasting and following administration of glucocorticoid hormone. The inhibition exerted by the cytosol on the three proteases was also differentially affected by precipitation with trichloracetic acid, heat, dialysis and molecular sieve chromatography. It is suggested that the intracellular protease inhibitor(s) are involved in the regulation of muscle protein degradation.