Myofibrillar protease activity in muscle tissue from patients in catabolic conditions.

Myofibrillar alkaline protease activity was shown to be present in human skeletal muscle. Endogenous myofibrillar proteins and 14C-labelled, exogenous haemoglobin were both active as substrates, and the enzymic activity appeared to be similar to the myofibrillar protease previously described in rodent muscles. The activity of this enzyme was determined in patients undergoing surgery for a variety of diseases. Significant elevations in proteolytic activity were found in the abdominal wall muscle of patients in wasting conditions as compared with non-catabolic diseases. In cachectic patients on total parenteral nutrition the protease activity was similar to reference values. The results imply that increased activity of the myofibrillar alkaline protease plays a role in the development of cachexia in human wasting diseases by prompting degradation of muscle proteins.