Properties of Euglena gracilis cytoplasmic ribosomes in salt

Abstract The properties of Euglena gracilis cytoplasmic ribosomes were studied as a function of monovalent salt. In 40 mM KCl, gel electrophoresis and sedimentation studies show a heterogeneous high molecular weight fraction and the monomer. The monomer sediments at s 20, w = 85 S. In 0.1 M KCl, the monomer dissociates into subunits which sediment at 62 S and 46 S. The high molecular weight fraction, which is ribonuclease sensitive and presumably the polyribosome fraction, remains stable. With increasing ionic strength, the monomer derived subunits continue to sediment in the regions of 60 S and 40 S up to 0.4–0.5 M KCl, where an abrupt transition occurs and sedimentation rates in 0.5 M KCl drop to 36 S and 28 S. Polyacrylamide gel electrophoresis protein patterns of 0.5 M KCl washed ribosomes were different from patterns of low salt washed ribosomes. In addition, the monomer, or the original subunit sedimentation rates, were not restored when the high salt washed ribosomes were placed back in low salt. Protein losses in high salt are presumed to be responsible for the major changes with high KCl washed ribosomes.