organic compound belonging to the purine family, occurring free in tea or combined in many substances of biological importance, including the nucleic acids (nucleic acid), which govern hereditary characteristics of all cells.

Partial decomposition of ribonucleic and deoxyribonucleic acids yields mixtures from which the compounds adenylic acid and deoxyadenylic acid, respectively, may be separated. These acids, called nucleotides (nucleotide), are phosphate esters of adenosine and deoxyadenosine, which are smaller units (nucleosides) composed of adenine and either ribose or deoxyribose. Compounds of adenine include vitamin B₁₂ as well as adenosine triphosphate and other coenzymes (substances that act in conjunction with enzymes).