Pfizer Handbook of Microbial Metabolites 560 



The occurrence of V-compound could be explained as due 

 to a side-reaction in which pyruvate rather than acetoin 

 reacted with the pyrimidine, or it may merely be an oxida- 

 tion product of G-compound. The close relationship be- 

 tween pyruvate, active acetaldehyde and acetoin, which is 

 mediated by thiamine, has been discussed in an earlier 

 section. 



The origin of the ribityl group remains obscure. It is 

 yet to be shown whether this moiety is derived from the 

 ribose of the purine nucleosides or whether it is formed in 

 some other way. Some work has been done on this facet 

 of the biosynthesis. ^'^ **• *^' ^'^ 



Riboflavin is phosphorylated by ATP to give riboflavin- 

 5'-phosphate, a coenzyme form. This, in turn, can react 

 again with ATP in the presence of the appropriate en- 

 zyme to form flavine-adenine dinucleotide, the other co- 



Mg++ 



Riboflavin -f ATP -^ Riboflavin-5'-phosphate + ADP 



Riboflavin-5'-phosphate -|- ATP :^ Flavine-adeninedinucleotide + Pyrophosphate 



enzyme form. Flavine-adenine dinucleotide (FAD) is 

 produced commercially in Japan from E. ashbyii my- 

 celium. 



The principal point of attachment of fiavinemononucle- 

 otide (FMN) to the apoenzyme seems to be the phosphate 

 group. There may be involvement of the 3-imino group 

 also. FAD is the most prevalent coenzyme form, although 

 FMN occurs in rather large proportions in some microor- 



44 G. W. E. Plaut and Patricia L. Broberg, /. Biol. Chem. 219 131 

 (1956). 



4=^ Edna B. Kearney and Sasha Englard, ibid. 193 821 (1951). 



4^ Anthony W. Schrecker and Arthur Kornberg, ibid. 182 795 

 (1950). 



