The role of enzyme degradation in enzyme turnover during tissue differentiation.

1. The role of enzyme degradation in enzyme turnover during tissue differentiation has been investigated by the use of equations based on the model of Berlin and Schimke (Mol. Pharmacol. 1 (1965) 149-156). 2. A digital computer has been used to calculate the change in enzyme amounts which would result from different changes in the rates of synthesis and degradation of an enzyme during cell differentiation. The energetics of these alternative processes have been compared. 3. The results demonstrate that changes in the rates of synthesis and degradation of an enzyme after a differentiation stimulus enhance the flexibility and rapidity of changes in enzyme amount during enzyme accumulation. Decreases in the rate of degradation of an enzyme during enzyme accumulation lead to a considerable saving of energy. 4. Hypotheses are proposed to account for the different modes of turnover of protein subgroups during cytodifferentiation in terms of specific changes in the rates of synthesis and degradation of the subgroups.