Hormonal and metabolic control of proteolysis.

Proteolysis in heart muscle is regulated by hormonal and metabolic factors. In the absence of insulin, protein degradation accelerated, autophagic vacuoles appeared within the heart and latency of lysosomal enzymes decreased. Addition of insulin prevented or reversed these changes. Provision of leucine inhibited proteolysis in control hearts. Addition of the products of transamination and oxidative decarboxylation of leucine, isoleucine and valine had similar inhibitory effects. Protein degradation was inhibited in ischaemic or anoxic hearts, but latency of lysosomal enzymes was decreased. Inhibition of degradation in energy-poor tissue may represent both an energy-requirement for proteolysis and inhibition by accumulation of metabolic products, such as lactate.