<n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>A series of heterocyclic compounds that are variously substituted in nature and are known also as purine bases. They include ADENINE and GUANINE, constituents of nucleic acids, as well as many alkaloids such as CAFFEINE and THEOPHYLLINE. Uric acid is the metabolic end product of purine metabolism.</n0:def-definition><n0:def-source>MSH2002_06_01</n0:def-source></n0:ComplexDefinition><n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>bicyclic ring structure consisting of fused imidazole and pyrimidine rings, with nitrogen atoms at the 1,3,7, and 9 positions; the basic structure of adenine, guanine, and other biologically important bases.</n0:def-definition><n0:def-source>CSP2002</n0:def-source></n0:ComplexDefinition><n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>One of two chemical compounds that cells use to make the building blocks of DNA and RNA. Examples of purines are adenine and guanine. Purines are also found in meat and meat products. They are broken down by the body to form uric acid, which is passed in the urine. High levels of uric acid in the body may cause gout.</n0:def-definition><n0:def-source>NCI-GLOSS</n0:def-source></n0:ComplexDefinition>