A Comparative Study of Basic, Acidic and Neutral Polypeptidyl RNases, Including Polyarginyl and Polyhistidyl Derivatives

The syntheses of poly‐l‐arginyl and of poly‐l‐histidyl RNase are described. Poly‐l‐arginyl RNase was obtained by guanidisation of poly‐l‐ornithyl RNase, which, in turn, was prepared from native RNase by reacting it with δ,N‐trifluoroacetyl‐α, N‐carboxy‐l‐ornithine anhydride, with subsequent removal of the trifluoroacetyl groups with piperidine. Derivatives enriched with up to 71 arginine residues were prepared and studied. Poly‐l‐histidyl RNase was prepared by the reaction of RNase with the unprotected N‐carboxy‐l‐histidine anhydride hydrochloride. Derivatives enriched with up to 22 histidine residues per RNase molecule were obtained. The enzymic activity of both poly‐l‐ornithyl RNase and poly‐l‐arginyl RNase towards cytidine‐2′,3′‐cyclic phosphate is only moderately affected by the attachment of the basic peptides. The activity on RNA is, on the other hand, strongly decreased in poly‐l‐ornithyl RNase and completely abolished in polyarginyl RNase, thus illustrating that the activity of the modified enzymes on these two substrates is affected independently. The pH of optimal activity of the basic polyarginyl RNase on cytidine‐2′,3′‐cyclic phosphate at low ionic strength was found to be increased in comparison to that of the native enzyme, while that of the acidic polyglutamyl RNase, the synthesis of which was previously described, was lowered. Polyhistidyl RNase was less active on RNA than the native enzyme, while its activity toward cytidine 2′,3′‐cyclic phosphate exceeded that of unmodified RNase. All the derivatives described recovered their full initial enzymic activity after complete reduction of the disulfide bridges followed by reoxidation.