Uric Acid Calculi

Uric acid is an end-product of purine metabolism. In most mammals the sparingly soluble uric acid is converted into the much more soluble compound allantoin by the action of the enzyme uricase. The first stage in purine biosynthesis is the formation of ribofuranosylamine-5-phos-phate from 5 phosphoribosyl-1-pyrophosphate, a reaction which is catalyzed by the enzyme phosphoribosylamino-transferase [28]. This irreversible step possibly determines the site of action of a feed-back control mechanism which enables the end-products (adenine and guanine ribonucleotides) to regulate the rate of their own production. Possibly some cases of primary hyperuricaemia and gout may result from a defect in this self-regulating mechanism.