candidate: They serve as sources of chemical energy ( adenosine triphosphate and guanosine triphosphate ) , participate in cellular signaling ( cyclic guanosine monophosphate and cyclic adenosine monophosphate ) , and are incorporated into important cofactors of enzymatic reactions ( coenzyme A , flavin adenine dinucleotide , flavin mononucleotide , and nicotinamide adenine dinucleotide phosphate ) .