SUMMARY: Reported sedimentation coefficients of bacterial ribosomes display noticeable variation. Since this might be due to differences in experimental conditions or to actual differences amongst the bacteria this problem needed re-investigation. The sedimentation coefficients of ribosomes from seven widely divergent bacteria (Streptomyces, Acetobacter, Pseudomonas, Azotobacter, Escherichia, Streptococcus and Bacillus) were determined by analytical ultracentrifugation. The bacteria were selected to cover nearly the entire range of molar guanine + cytosine content of DNA. Correction for pressure and dilution was always negligible; correction for temperature was eliminated by working directly at 20·0°. The correction for concentration was the most important one. Further reduction to standard conditions (from dilute buffer to water) resulted in a change of about 3%. The corrected sedimentation coefficients, expressed as ( , w)0, were nearly the same for all these bacteria, being in the ranges 29·5±2, 37·5±2·8, 56·3±1·9, 76·7±2·5, 110·5±1·6 × 10 sec. It thus seems unlikely that these coefficients will be useful as an aid in bacterial taxonomy. Disruption of samples of the same bacterial suspension by ultrasonic treatment or with the French pressure cell frequently resulted in quantitative, and sometimes qualitative, differences in the yield of ribosomes.


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