Free and membrane-bound ribosomes in regenerating rat liver

A simple double-isotope technique is described which permits a detailed comparison of free and membrane-bound ribosomes isolated from ''co-homogenates'' of livers from partially hepatectomized and sham-operated animals. It is shown that 48 h after partial hepatectomy, a time at which liver cell proliferation is proceeding at a maximal rate, there is indeed a striking shift in ribosome distribution resulting in about a 40% rise in the proportion of free ribosomes. Over the same interval the absolute concentration of hepatic ribosomes increases markedly with the result that the total number of free ribosomes per unit mass of regenerating tissue rises to nearly double that in normal liver. The observed shift to favor a substantial increase in the concentration of free ribosomes is consistent with an enhanced need in regenerating liver for the synthesis of proteins destined for intracellular use. It is suggested that the method described here, which permits sensitive and precise comparison of the distribution of free and membrane-bound ribosomes in paired tissue samples, may find useful application in other systems as well. (Auth.)