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Ribonucleinase. III. The Behavior of Copper and Calcium in the Purification of Nucleic Acid and the Effect of These and Other Reagents on the Activity of Ribonucleinase.--CHARLES A. ZITTLE (Journal of Biological Chemistry, I63 : I I I, I946). Copper and calcium,
both present in commercial nucleic acids, accompanied the insoluble high polymer fraction when a nucleic acid solution was precipitated with acetic acid. Copper inhibited ribonucleinase, and when the amount of copper present in the crude nucleic acid was relatively large it became noticeably inhibitory when the precipitated nucleic acid was used as the substrate for ribonucleinase. The presence of calcium apparently had no effect on ribonucleinase. A substance was present in some lots of nucleic acid which prevented the inhibition of ribonucleinase by copper until a certain concentration of copper was exceeded. Copper and zinc apparently inhibit by the formation of an inactive dissociable complex with the enzyme. Zinc was almost as inhibitory as copper; other metals tested had a negligible effect; phenylmercuric acetate was inhibitory. Iodoacetate and iodoacetamide, -SH reagents, also inhibited ribonucleinase. Contrary to the action of each on other enzymes, iodoacetic acid was more inhibitory than iodoacetamide. Arsenite, selenite, cystine, and maleic acid had no effect on ribonucleinase.
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the cause of the alteration in properties. Another possible cause may be that the acid group liberated by the nuclease (1) concerns the adenine radical and that some other alteration in the nucleic acid molecule prevents the initial hydrolysis by the nuclease necessary for the eventual liberation of