It now devolves upon us to note the arrangement of the atoms in the purin nucleus. To each atom is affixed a number indicating the exact location of the various atoms and groups attached to the said nucleus. The manner in which the various purin bodies are built up around the purin nucleus C₅N₄ will become apparent from a study of the following structural formulæ culled from Wells’ “Chemical Pathology”:—
Structural Formulæ
To describe the individual derivatives of purin we have to indicate to which particular atom of the purin nucleus the combining groups are attached. Thus, for example, adenine in structure is classed as a 6-amino-purin, and accordingly has the following formula:
Other important bodies built up round the purin nucleus C₅N₄, variously designated as xanthine, alloxuric and nuclein bodies:—
It will be seen that the purin bases stand in very close chemical relationship to uric acid in that the latter also is marked by the possession of a group called the purin nucleus; indeed, the relationship of uric acid to the purin bases is more intimate than to urea (CON₂H₄), close though this latter be as may be seen from the study of its constitutional formula. (For uric acid may be regarded as composed of two urea radicles, linked by a tricarbon chain. By oxidation and hydrolysis, two molecules of urea may be obtained from one of uric acid, and conversely uric acid is produced by the condensation of urea with hydroxy acids).