Mechanisms of degradation of myofibrillar and nonmyofibrillar protein in heart.

The degradation of cardiac proteins is known to be altered by many physiological and pathological interventions, but the precise intracellular processes that regulate proteolysis and the relative roles of different proteolytic pathways in degrading different classes of protein remain poorly understood. Agents that interfere with lysosomal function produce major decreases in total protein breakdown; thus, lysosomes and lysosomal proteinases seem to be important in proteolysis. However, these same agents cause no change in the degradation of myofibrillar proteins, suggesting that this class of proteins is not dependent on lysosomal pathways for its turnover.