Breakdown of proteins from mouse liver subcellular fractions. Effect of nutritional changes

The rapid restoration of liver protein mass observed in protein-depleted mice when they are fed with an adequate diet is quantitatively explained by a large decrease in the average rate of breakdown of total liver proteins. This study was performed in order to know whether this inhibition of breakdown affects in the same way all the protein constituents of the tissue, or only affects a group of these proteins belonging to a particular subcellular fraction. Subcellular fractions were obtained by differential centrifugation. The relative rates of breakdown of their proteins were estimated by the conservation of radioactivity in these proteins previously labelled by the administration of NaH14CO3 to mice. The results obtained indicated: 1) a general decrease in the rate of breakdown of proteins of subcellular fractions from re-fed livers compared with livers of protein-depleted mice; 2) a decrease of breakdown of proteins from cytosol in re-fed mice which is higher as lower is the molecular weight of the proteins subunits.