Fig. 7

Structures of riboflavin, guanosine triphosphate (GTP), and guanine. GTP shares nine of its ten carbon atoms with riboflavin. Guanine shares all five carbon atoms with GTP and four of those with riboflavin. Only the xylene ring (white circles in riboflavin) is the structurally exclusive unit only found in the vitamin compared to the other two compounds. Grey circles denote carbon atoms that are shared between GTP, guanine, and riboflavin