Xanthine (Standard) is a reference standard for research and analysis in studies involving Xanthine. Xanthine (Isoxanthine) is a product on the pathway of purine degradation. Xanthine is subsequently converted to uric acid by the action of the Xanthine oxidase enzyme. Xanthine is found in most body tissues and fluids in various organisms. Biologically Xanthine is produced from guanine by cypin (guanine deaminase). Furthermore, Xanthines act as antagonists for adenosine receptors, with selectivity depending on whether there are substitution of alkyl groups.