The Discovery of Purins

Miescher, who had already isolated nuclein and nucleic acid, came nigh to one other equally important discovery. Heating a specimen of protamine with nitric acid, he noted that a yellow spot formed which turned to bright red when moistened with alkali.

Alive to the import of the reaction, Miescher requested Piccard to examine salmon sperm for purin bases. Extracting the same with hydrochloric acid, Piccard found guanine, and what he thought was hypoxanthine, but which was in truth adenine.

Another distinguished worker in this sphere, Kossel, noted that, subjected to the action of hydrolytic agents, nucleins always yield purin derivatives; also that the same were derived, not from the protein of the nuclein, but from the nucleic acid. Thus it was to Kossel that we are indebted for the discovery of the purin bases, hypoxanthine, xanthine, guanine, and lastly adenine. It was, indeed, through his brilliant achievements that nucleic acid became recognisable as a definite entity, distinguishable from proteins and other body elements, this latter differentiation by token of the purin bases which are contained in nucleic acid.

Moreover, it led to the dissipation of the old belief that uric acid was an intermediate product of protein metabolism, for the revelation of purin bases as decomposition products of nucleic acid carried with it the inference that uric acid also had chemical affinities therewith. The chemical structure of the purin bases and that of uric acid betrayed a common likeness, and, therefore, a presumptive physiological connection; in other words, that a chemical nexus obtained between the cell nucleus or nucleic acid and uric acid.

The physiological derivation of uric acid from nucleic acid did not long lack experimental proof. In 1886 Minkowski found that, given extirpation of their livers, the urine of birds contained ammonium lactate, evidently a substitute for the uric acid normally present, notwithstanding the uric acid never entirely disappeared from the urine. This indicated the derivation of uric acid from two sources:—

To clear up the obscurity regarding the latter, V. Mach, after extirpating the livers of geese, injected them subcutaneously with hypoxanthine, finding that the same was converted into uric acid, which was excreted in the urine. In this way the capacity of the organism to elaborate uric acid from a purin precursor was demonstrated.