it became evident that the nucleoside, riboflavin, does not itself represent the original active group of the flavoprotein; it must be considered a breakdown CH a I N NH. N N H~ C "/\/ ""-C- O H3~( V " C=O 3 II I 1 - 3 H ~ " ff . . . . . . . . . . . / NH H3CJJ"N)"C/~m N?' C II II o o lumichrome lumiflavin product of a naturally occurring flavin nucleotide. Riboflavin-5'-phosphate (FMN, for flavin mononucleotide; see formula) was indicated by THEORELL as the original active group. In 1938, WARBURG and CHRISTIAN (1938 [7]-[10]) / OH ,CH CHOH- CHOH- CHOH-CH -P" 0 2- 20 N ,N OR H~A/ V " C-O 3 II I 1 - 3 H ~/"W,7'''C/NH II o Riboflavin-5'-phosphoric acid could bring excellent evidence for the idea that the co-enzyme of another flavo protein, n. amino acid oxidase, isflavin-adenine-dinucleotide or FAD (see formula). This was supported by ABRAHAM (1939), who identified both FMN and adenosine 5'-phosphate as hydrolysis products of FAD. The discovery of the coenzyme role of FAD has induced WARBURGand coworkers to engage in some speculation concerning the possibility that FMN is itself an artifact, produced through a breakdown of FAD. This aspect will be discussed later, in connection with recent work done on OYE in THEORELL'S laboratory. o NH 2 N CH3 .
