Partial P1 nuclease digestion of 5′‐32P‐labeled tRNAs, followed by polyacrylamide gel electrophoresis and autoradiography. results in a series of bands of unequal intensities. Comparison of the digestion profiles of two conformers of yeast tRNALeu3 shows that P1 nuclease is sensitive to structural features of its substrate, Examination of the digestion pattern of yeast tRNAPhe in light of its known three‐dimensional conformation shows that the enzyme's activity reflects the primary, secondary and tertiary levels of tRNA structure.

The sensitivities of the binding step and the lytic step of haemolysis by pneumolysin to the action of various inhibitors and to variations in the assay conditions were studied. Binding was inhibited by HgCl, and N-ethylmaleimide. Lysis by previously fixed lysin was insensitive to HgCl, and only slightly sensitive to N-ethylmaleimide. Binding of pneumolysin was independent of ionic strength. Binding of pneumolysin and streptolysin 0 decreased above pH 8.0 and 8.4, respectively. These results suggest that binding requires a non-ionized unsubstituted sulphydryl group. Incubation of erythrocytes with NaF caused inhibition of pneumolysin, indicating that some metabolic function of the cell may be involved in lysis. The action of streptolysin 0 was not affected by NaF.

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