Studies on the Correlation between Size and Relative Degradation Rate of Soluble Proteins

There is a general correlation between the relative degradation rate and the size of soluble proteins from rat liver. The subunit size rather than the multimer size appears to influence the rate of degradation, since subunits which make up multimers of a single size range are degraded at heterogeneous rates with larger subunits being degraded more rapidly than smaller ones. Soluble proteins which are degraded more rapidly in vivo tend also to be more susceptible to proteolysis in vitro with either Pronase or trypsin. Furthermore, there is a general correlation between the molecular size of soluble proteins, as determined by Sephadex chromatography, and their in vitro susceptibility to proteolysis. These results suggest that the relative degradation rates of soluble proteins are determined at least in part by their inherent susceptibility to proteases. The correlation between size and relative rate of degradation in vivo is also present for soluble proteins from rat kidney, testes, brain, and muscle, and from HeLa cells and pea stem sections. These findings indicate that the correlation between size and degradation rate may be a general characteristic of intracellular protein degradation in eukaryotes.