DISSOCIATION OF RAT LIVER RIBOSOMES BY ETHYLENEDIAMINETETRAACETIC ACID - MOLECULAR WEIGHTS CHEMICAL COMPOSITION AND BUOYANT DENSITIES OF SUBUNITS

Rat liver ribosomes were dissociated to subunits by the addition of EDTA and the subunits were separated by sucrose gradient centrifugation in a zonal rotor. Transfer ribonucleic acid, 5S ribosomal ribonucleic acid, and a “7S” ribonucleic acid were found in a slowly sedimenting peakwhich also contained proteinlike material, presumably nascent peptides. For molecular weight measurements with absorption optics by high-speed equilibrium centrifugation, the isolated subunits were fixed with 1% formaldehyde at pH 7.4. Partial specific volumes were calculated fromthe protein and ribonucleic acid contents of the subunits as determined by chemical analysis and from theirbuoyant densities in CsCl after formaldehyde fixation. The large subunit had a molecular weight of 3.1 million daltons and contained 45% protein; in 0.03 m KCl-0.001 m potassium phosphate (pH7.0)-0.2 mM MgCl2 it had a sedimentation coefficient, s20,w0, of 50 S. The small subunit had a molecular weight of 1.2 million daltons and contained 50% protein. Its sedimentation coefficient was 29 S. The buoyant densities of the large and small subunits were 1.602 and 1.593 g per ml in CsCl and 1.442 and 1.425 g per ml in CS2SO4. © 1969, American Chemical Society. All rights reserved.