Conditions Affecting the Dissociation Reaction in vitro of Rat‐Liver Ribosomes

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Abstract
Subunits were obtained by incubation of ribosomes with cell sap, puromycin, GTP, phospho‐enolpyruvate, pyruvate kinase, subsequent exposure to 0.15 M KCl and 1 mM MgSO4 followed by sucrose density‐gradient separation.Addition of ATP reduced the yield of the subunits but had no influence on their purity as judged by polyacrylamide‐gel electrophoretic analysis of their RNA. Reassociation of the sub‐units to form 80‐S ribosomes and restoration of polyuridylic‐acid‐dependent synthesis of polyphenylalanine was highest when the subunits were prepared by incubation of ribosomes in the absence of ATP with or without puromycin.In the absence of puromycin, the dissociation rate per minute was 8% and 2% of the total at 35° and 25°C, respectively.Dietary protein restriction excerted no influence on the dissociation of the ribosomes incubated with cell sap of liver from rats fed a normal protein diet, while cell sap from protein‐restricted rats had a decreased capacity to dissociate ribosomes of normal rats. These differences were significant per wet weight of liver but not per mg cell‐sap protein, due to a simultaneous decrease in the protein content of the cell.