Proteolytic activities in kidney and liver during refeeding of protein depleted mice.

Proteolytic activities at pH 5.0 and pH 7.4 in both kidney and liver during refeeding of protein-depleted mice were determined. Under this nutritional condition, the in vivo rate of protein breakdown is inhibited. Protein depletion caused in both kidney and liver a loss of pH 5.0 proteolytic activity. It was restored to normal values after 12 hours of refeeding with a complete diet. The pH 7.4 proteolytic activity also decreased as a consequence of protein depletion, but remained low during refeeding. Both re-fed kidney and liver lysosomes showed an increased stability to osmotic shock and, therefore, a decreased autophagic activity. The results indicate that both kidney and liver exhibit a similar behavior. The decreased activity of the lysosomal-vacuolar system, and the low pH 7.4 proteolytic activity may account for the observed in vivo protein breakdown inhibition during refeeding of protein-depleted mice.