Xanthine Calculi and Xanthinuria

Xanthine is a purine base and is closely related to hypoxanthine and uric acid. The main precursor of xanthine is inosinic acid, a substance which, if it is synthesized by the body to an amount in excess of that needed for nucleoprotein synthesis, can be metabolized ultimately to uric acid by one of three pathways: (1) by way of xanthylic acid and xanthosine (2) by way of guanylic acid, guanosine and guanine by irreversible deamination; or (3) by way of hypoxanthine by irreversible oxidation, a route which requires the presence of xanthine oxidase. These bases are derived by the action of -purine nucleoside Phosphorylase, from their respective nucleosides; the same enzyme breaks down inosine.