Characterization and stability of ribosomes from mesophilic and thermophilic bacteria

Ribosomes were isolated from three mesophilic and three thermophilic strains of Bacillus. The ribosomes consisted of about 55% protein and 45% ribonucleic acid. Average ratios for the absorbance at 260/235 and 260/280 mmu were 1.77 and 1.92 for the mesophiles and 1.63 and 1.84 for the thermophiles. Ultracentrifugation revealed mainly components with sedimentation coefficients of about 30, 50, 70, 100, and 120S. All the preparations were shown to contain a ribonuclease which, in the presence of ethylenediaminetetraacetic acid, led to ribosome breakdown as measured by the increase in acid-soluble nucleotides. The stability of the ribosomes from the thermophiles was consistently greater than that of the ribosomes from the mesophiles. After 5 hr at 37 C, the breakdown was about 80% for the ribosomes from the mesophiles and 55 to 70% for those from the thermophiles. At 60 C, the ribosomes from the mesophiles were broken down slightly more and at a faster rate than those from the thermophiles. At temperatures above 60 C, the breakdown was again more pronounced for the ribosomes from the mesophiles.