Mode of Action of “Ribonuclease.”

Abstract

A thermostable enzyme, first noted by Jones 1 to be present in the pancreas, has received recent attention at the hands of Dubos and Thompson, 2 Schmidt and Levene, 3 Kunitz, 4 and Allen and Eiler. 5 Dubos and Thompson found the enzyme to effect the decomposition of ribonucleic acid from yeast. The enzyme was noted to be without action on the following substances: desoxyribonucleic acid from thymus, egg albumin, hemoglobin, Witte's peptone, a number of plant, animal, and bacterial polysaccharides, ethyl acetate, tributyrin, and an ether-soluble fraction extracted from pneumococci.

The enzyme was named “ribonuclease”and claimed not to be a phosphatase. Schmidt and Levene describe the action of the enzyme to be that of a depolymerase, and consider the name “ribonucleodepolymerase”to offer a more appropriate description of the mode of action. Kunitz has isolated the enzyme in the crystalline state, and claims that its mode of action appears to correspond to the nuclease activity described by Dubos and Thompson. Allen and Eiler have shown that the enzyme effects the liberation of an acidic group of ribonucleic acid. Titration data place the liberated acidic group in the range of a secondary phosphoric acid dissociation. An examination of the structures of the known components of the ribonucleic acid molecule shows that the secondary hydroxyl of the phosphate group conceivably may be linked with any of the following reactive groups: (a) the hydroxyl group of guanine or uracil; (b) the amino group of guanine, adenine, or cytosine: (c) the hydroxyl group of position 5 or of position 2 of the ribose; (d) the hydroxyl of another phosphate group. This last possibility, seemingly, is ruled out by the data of Allen and Eiler. However, the indications are that certain characteristics of the action of the enzyme are those of a phosphatase.