Photolytic and enzymatic transformations of pteroylglutamic acid.

Bloom et al. (1) found that ultraviolet light converted pteroylglutamic acid (PGA) which is not fluorescent into a fluorescent material. Stokstad, Fordham, and de Grunigen (2) observed that sunlight caused the liberation of a diazotizable amine, indicating that cleavage had occurred between the pterine and the p-aminobenzoylglutamic acid components. As part of a search for a sensitive analytical reaction for PGA, this photolytic effect has been further investigated, and a rather interesting sequence of transformations has been found to occur. Evidence to be presented below indicates that when PGA (I) is irradiated with ultraviolet light it is first converted to 2-amino-4-hydroxy-6-formylpteridine (II) and a diazotizable amine. With further irradiation the aldehyde is converted to the corresponding 6-carboxylic acid derivative (III) and finally to the decarboxylated 2-amino-4-hydroxypteridine (AHP) (IV). This, in turn, is susceptible to oxidation to isoxanthopterin (V) by an enzyme present in cream, which is probably identical with xanthine oxidase and xanthopt,erin oxidase.