1. The ;30s' and ;50s' ribosomes from ribonuclease-active (Escherichia coli B) and -inactive (Pseudomonas fluorescens and Escherichia coli MRE600) bacteria have been studied in the ultracentrifuge. Charge anomalies were largely overcome by using sodium chloride-magnesium chloride solution, I 0.16, made 0-50mm with respect to Mg(2+). 2. Differentiation of enzymic and physical breakdown at Mg(2+) concentrations less than 5mm was made by comparing the properties of E. coli B and P. fluorescens ribosomes. 3. Ribonuclease-active ribosomes alone showed a transformation of ;50s' into 40-43s components. This was combined with the release of a small amount of ;5s' material which may be covalently bound soluble RNA. Other transformations of the ;50s' into 34-37s components were observed in both ribonuclease-active and -inactive ribosomes at 1.0-2.5mm-Mg(2+), and also with E. coli MRE600 when EDTA (0.2mm) was added to a solution in 0.16m-sodium chloride. 4. Degradation of ribonuclease-active E. coli B ribosomes at Mg(2+) concentration 0.25mm or less was coincident with the formation of 16s and 21s ribonucleoprotein in P. fluorescens, and this suggested that complete dissociation of RNA from protein was not an essential prelude to breakdown of the RNA by the enzyme. 5. As high Cs(+)/Mg(2+) ratios cause ribosomal degradation great care is necessary in the interpretation of equilibrium-density-gradient experiments in which high concentrations of caesium chloride or similar salts are used. 6. The importance of the RNA moiety in understanding the response of ribosomes to their ionic environment is discussed.

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A test-tube method is described for the determinations of L-asparaginase and L-glutaminase in suspensions and extracts of bacteria. An automated modification of the method was used to determine the asparaginase activities of about 200 strains from 78 species and the glutaminase activities of 46 strains from 13 species. Both enzymes were widely distributed and, at pH 8-5, asparaginase was generally the more active. Asparaginase was exceptionally active in some species of Erwinia.

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