But before proceeding to consider in detail the complex series or enzymatic transformation that this entails, it will, I think, be wiser to deal first with the chemistry of uric acid, its solubilities, and its sources, whether exogenous, endogenous or synthetic.
The Chemistry of Uric Acid and the Purin Bodies
Much of the vague philosophy of disease in past times may fairly be attributed to the complexity and mystery of action inherent in living matter. The subjects of physics, chemistry and biology, in their wider acceptation, were unevolved, and scientific pathology, the offspring of this ancestry, was yet unborn. How much we owe to physics, chemistry, and biology, those handmaids of medicine, is inestimable! But something at least of our debt thereto will be revealed in the following pages.
Of the purins in human urine, the most important is uric acid, and far behind comes xanthine, while traces of hypoxanthine, guanine, and adenine are also detectable. Some years ago the current view was that the metabolism of any protein gave rise to uric acid. This assumption has now proved to be erroneous, for it is known that only certain foodstuffs lead to an increase in the uric acid excretion; in other words, on a diet rich in purin the output thereof is considerably higher than on a purin-free diet, this being due to the large amount of nuclein and purin bases in flesh foods, especially those containing glandular substances. Under ordinary conditions the excretion of uric acid ranges from 0·3-1·2 gm. per diem, or 0·02-0·10 per cent. The oscillations in output vary with the state of health, diet, and personal idiosyncrasy.
Chemical Constitution
The empirical formula of the uric acid molecule, C₅H₄N₄O₃, has for long been known, but it was reserved for Emil Fischer to reveal the chemical structure thereof. Through his labours we now know that uric acid is one of a group of substances which owe their kinship to their possession in common of the heterocyclic ring termed by Fischer the “purin nucleus” (1898).
The intimate relations of the purins of bio-chemical interest to the purin nucleus, and alike to each other, will be rendered more intelligible by examination of their structural formulæ as hereafter given. All, as will be seen, are derivatives of a synthetically formed body purin which, though unimportant in itself, is yet interesting in that it is the basic substance from which the following take origin:—
| Purin | C₅H₄N₄ | |||
| Hypoxanthine | C₅H₄N₄O | Monoxy-purin | } | |
| Adenine | C₅H₃N₄NH₂ | Amino-purin | } | |
| Xanthine | C₅H₄N₄O₂ | Dioxy-purin | } | Purin Bases. |
| Guanine | C₅H₃N₄ONH₂ | Aminooxy-purin | } | |
| Uric acid | C₅H₄N₄O₃ | Trioxy-purin | } |