puriineihin

Purines are a class of nitrogenous bases used in nucleic acids, characterized by a fused bicyclic ring system. The two main purine bases in DNA and RNA are adenine and guanine.

In nucleotides, purines form the bases of DNA and RNA and also occur in energy carriers such as ATP and GTP, as well as in signaling molecules like cAMP and cGMP.

Purine metabolism includes de novo synthesis and salvage pathways. De novo synthesis starts from ribose-5-phosphate and builds the purine ring attached to the sugar phosphate, eventually producing inosine monophosphate (IMP), the branch point for adenine and guanine nucleotides. The salvage pathways reuse free purine bases to form nucleotides, primarily via enzymes such as APRT and HGPRT.

Purine degradation in humans ends with uric acid, which is excreted in urine. Hypoxanthine and xanthine are intermediate products; the enzyme xanthine oxidase catalyzes oxidation steps to uric acid.

Clinical relevance includes conditions related to purine metabolism. Hyperuricemia can lead to gout, a form of inflammatory arthritis. Hereditary HGPRT deficiency causes Lesch-Nyhan syndrome, with neurological symptoms and excessive uric acid production. Dietary purines—found in meats, certain fish, and some beverages—can influence uric acid levels in susceptible individuals, though effects vary.

Purines are universal across life, with purine nucleotides serving as essential components of DNA, RNA, energy transfer, and intracellular signaling. The biosynthesis and turnover of purines are thus central to metabolism and health.