INFLUENCE OF PROTEIN NUTRITION ON PROTEOLYTIC ACTIVITY AND HISTONE CONTENT IN ISOLATED MOUSE-LIVER NUCLEI

The proteolytic activity in isolated liver nuclei from mice subjected to different conditions of protein nutrition and its relationship with histones metabolism was studied. After five days of protein depletion , the nuclear azocaseinolytic activity increases concomitantly with a decrease in the concentration of histones. This activity resembles, in localization, optimum pH and inhibition behavior to rat liver chromat in neutral proteinase that degrades histones. Moreover, these proteins were identified as its main endogenous substrates. Refeeding of the p rotein depleted mice for 16 h with a normal diet was unable to either diminish proteolytic activity or recover the normal histone level. Act ivity of the multicatalytic proteinase complex (proteasome) was not de tected in nuclei. Furthermore, treatments known to activate this enzym e were ineffective. Taken together, these results suggest that nuclear proteases are mainly involved in the regulation of histone levels.