purine, type of organic base found in the nucleotides and nucleic acids of plant and animal tissue. The German chemist Emil Fischer did much of the basic work on purines and introduced the term into the chemical literature in the early 20th cent. The two major purines of almost universal distribution in living systems are adenine and guanine.

Any of a class of heterocyclic compounds with a two-ring structure composed of carbon and nitrogen atoms. The simplest member, purine itself (C₅H₄N₄), is not common, but its derivatives with the structure are. Examples are uric acid, caffeine, and two of the nucleotides in nucleic acids, guanine and adenine.

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