Purin

Purin, a term used in several languages for purine, refers to a family of heterocyclic aromatic compounds that form the core of many biologically important molecules. In English, purine is the standard term. Purines are bicyclic structures composed of a pyrimidine ring fused to an imidazole ring. The most familiar purine bases are adenine and guanine, which are key components of DNA and RNA. Hypoxanthine and xanthine are related purine bases, and uric acid is the end product of purine catabolism in humans.

Biological roles of purines are diverse. Purine nucleotides such as ATP and GTP store and transfer energy, participate in signaling, and serve as substrates for RNA and DNA synthesis. Purine cofactors, including NAD and FAD derivatives, participate in redox reactions and metabolism. Purines are maintained in the cell by two main paths: de novo synthesis, starting from ribose-5-phosphate and PRPP, and salvage pathways that recycle purine bases; the committed step in de novo synthesis is catalyzed by glutamine-PRPP amidotransferase. Catabolism converts purines to xanthine and uric acid, which are excreted.

Purinergic signaling is another facet of purin biology. Extracellular purines such as ATP and adenosine act on purinergic receptors (P1 and P2) to regulate processes including neurotransmission, inflammation, and vascular tone.

Clinical relevance includes disorders of purine metabolism. Gout results from hyperuricemia due to excess purine degradation. Lesch-Nyhan syndrome arises from deficiency of HGPRT, a key salvage enzyme, leading to neurologic and behavioral symptoms. Adenosine deaminase deficiency can cause severe combined immunodeficiency by disrupting purine metabolism.

Dietary purines occur in many foods, with higher levels in certain meats and seafood; in susceptible individuals, high purine intake can raise uric acid levels.