CHARACTERIZATION OF RIBOSOMAL AGGREGATES ISOLATED FROM LIVER

Abstract

Most of the ribosomes in rat liver sediment in weak centrifugal fields with nuclei and mitochondria. These ribosomes are presumably bound to large pieces of endoplasmic reticulum and have been studied relatively little. Following deoxycholate treatment, in contrast to the larger polyribosomes isolated from postmitochondrial supernatant fractions, they are isolated almost exclusively as pairs with an S20, w of 114. A simple technique of portal vein infusion permitted the study of in vivo incorporation of radioactive compounds over very short time intervals (30 sec or less). These studies, as well as studies of in vitro amino acid incorporation showed that the ribosomes associated with the more rapidly sedimenting cell fractions are responsible for the bulk of the protein synthesis in the liver. In contrast to the ribosomes in the postmitochondrial supernatant fraction, those in the more rapidly sedimenting cell fractions lose their ability to incorporate amino acids in vitro when isolated from their membranes by the standard sodium deoxycholate [DOC] technique. This is not due to any intrinsic abnormality of these ribosomes and would suggest that DOC treatment may in some way separate them from their messenger RNA.