One of the two major purines (the other is guanine) found in both RNA and DNA, and also in various free nucleotides of importance to the body (e.g., AMP (adenylic acid), ATP, NAD+, NADP+, and FAD); in all these smaller compounds, adenine is condensed with ribose at nitrogen-9, forming adenosine. For structure, see adenylic acid. SYN: 6-aminopurine.