Effects of potassium deficiency on mammalian ribosomes

Abstract

1. 1. When ribosomal monomers from rabbit reticulocytes or mouse ascitic tumor cells were dialyzed against K +-free media, they were transformed into highly ribonuclease-sensitive particles with a sedimentation velocity approximating that of large subunits. Only small amounts of free 40-S subunits were formed. The transformation, which had a pH optimum about 7.7, was not spontaneously reversed when the K + concentration was restored. Transformed particles had no activity of poly U-dependent phenylalanine incorporation. 2. 2. The ribosomes were markedly stabilized by K + already at a concentration of 0.5–1.0 mM. NH + 4, and particularly Tl +, were effective substitutes. On the other hand, equimolar amounts of extra MgCl 2 has essentially no effect. 3. 3. Polyribosomes were less sensitive than ribosomal monomers to K + deficiency. However, in K +-free media the sedimentation profile of polyribosomes gradually altered in a characteristic fashion, suggesting a formation of mixed aggregates of normal and structurally altered ribosomes. The activity of these polyribosomal suspensions of endogenous amino acid incorporation was still fairly high, and their structurally altered components seemed to revert to their normal conformation during incubation. 4. 4. It is concluded that the importance of K + for the structure of animal ribosomes is of the same order as that of Mg 2+. Although both ions are needed for a normal interaction between the ribosomal subunits, they are not mutually replacable, and seem to have different sites of action.