EFFECT OF P-MERCURIBENZOATE ON ULTRACENTRIFUGAL BEHAVIOR OF RAT LIVER RIBOSOMES

When rat liver ribosomes were isolated in the presence of 0.006 M β-mercaptoethanol and dialyzed against 0.05 M Tris-0.025 M KCl-2.5 mM MgCl2 (pH 8.3 at 5°), most of them aggregated to dimers and larger particles. They were then treated with 0.5-5.0 mM p-mercuribenzoate for 1-25 hr, at 5 or 25°, and examined in the analytical ultracentrifuge at 5°. As the reaction progressed ribosomal subunits appeared, and the sedimentation coefficients of the various components increased; the final values of s for the small subunit, large subunit, and ribosome were 13, 3, and 6% above the initial values. At 5°, after 6 hr in 5.0 MM p-mercuribenzoate, most of the larger particles and dimers had been disaggregated; the preparation consisted of a 108S component, single ribosomes, and about 40% of subunits. Liver ribosomes were much less sensitive than bacterial ribosomes. At 25° both the increase in sedimentation coefficients and the dissociation were more rapid, and the dissociation was much more extensive, than at 5°. Dissociation was only partially reversed by dialysis against 0.02 M β-mercaptoethanol. © 1969, American Chemical Society. All rights reserved.