riboflavin

(vitamin B2) A flavin pigment that has been implicated both in the perception of the phototropic stimulus and in photooxidation of endogenous auxins. It consists of an isoalloxazine ring substituted with the sugar alcohol ribitol. In its active phosphorylated form riboflavin phosphate, otherwise known as *FMN , it acts as a coenzyme for various oxidizing enzymes. Riboflavin is not synthesized by animals. See also FAD , vitamin.