In the latter instance a hydrolysing enzyme, xanthosine-hydrolase, by its action, splits off xanthine. We see, therefore, that by either route the end-product is the same. Following a like series of changes, the adenine radicle is transmuted into hypoxanthine. This either directly by the action of adenase:—
or indirectly through the agency of adenosine-deaminase, the hypoxanthine-glucoside (inosine) is formed, and subsequently the hypoxanthine is split off.
Xanthine and hypoxanthine are, therefore, now to hand, and given the presence of oxygen, their oxidation to uric acid ensues:—
Now, in man and the anthropoid apes, uric acid is the end-product of purin catabolism. In contrast therewith in most mammals only a minimal amount of the exogenous or endogenous purins escapes in the urine as uric acid. Most of it undergoes further oxidation into allantoin,[15] this change taking place in most mammals chiefly in the liver. According to Schittenhelm, if nucleic acid be given to dogs, pigs or rabbits, from 93-95 per cent. thereof appears in the urine as allantoin, and only 3-6 per cent. as uric acid, and 1-2 per cent. as purin bases.
Disruption of Nucleic Acid Molecule (Amberg and Jones).
