puriinit

Puriinit are a class of nitrogen-containing heterocyclic compounds that form one of the fundamental categories of nucleobases in biological nucleic acids. The purine nucleus is a fused bicyclic ring consisting of a pyrimidine ring fused to an imidazole ring. The most common purine bases in biology are adenine and guanine, which are components of RNA and DNA as nucleobases and also serve as the bases for nucleotides such as ATP and GTP.

In DNA and RNA, purine bases pair with pyrimidine bases: adenine pairs with thymine in DNA or uracil in RNA, and guanine pairs with cytosine. The base-pairing properties contribute to the structure and fidelity of genetic information, while purine nucleotides also function as energy carriers (ATP, GTP) and signaling molecules (cAMP, cGMP).

Biosynthesis and metabolism: De novo purine biosynthesis starts with ribose-5-phosphate, which is converted to phosphoribosyl pyrophosphate (PRPP) and proceeds through a sequence of enzymatic steps using amino acids such as glycine, glutamine, and aspartate to form inosine monophosphate (IMP), a branch point for AMP and GMP. Salvage pathways recycle hypoxanthine and guanine via HGPRT to regenerate IMP or GMP. Purine catabolism in humans ends with uric acid, excreted by the kidneys; many non-primate mammals convert uric acid to allantoin. Excess uric acid can lead to hyperuricemia and gout.

Clinical relevance and pharmacology: Diets high in purines may raise serum uric acid, influencing gout risk. Genetic disorders like Lesch-Nyhan syndrome result from HGPRT deficiency. Pharmacologic interventions include xanthine oxidase inhibitors such as allopurinol and febuxostat to lower uric acid, and immunosuppressants that target purine synthesis, such as mycophenolate mofetil (IMP dehydrogenase inhibitor) or purine analogs like azathioprine and 6-mercaptopurine. Purine metabolism is fundamental to energy transfer (ATP, GTP) and signaling (cAMP, cGMP).