PTERINE OXIDASE

Abstract

When pteroylglutamic acid (PGA) is irradiated with ultraviolet light, oxidative cleavage occurs and three pteridines are formed in succession (1). It was observed that the last of the series, 2-amino-4-hydroxypteridine (AHP), could be oxidized to isoxanthopterin by a concentrate of xanthine oxidase from cream. It was also observed that the first photolytic product, 2-amino-4-hydroxy-6-formylpteridine, was a remarkably effective inhibitor of this enzymatic oxidation. As little as 2 X lQ-* y of the aldehyde per ml. produced demonstrable inhibition (1). This enzyme and this inhibition have been further explored and it appears that a single enzyme in cream is responsible for the oxidation of xanthine, xanthopterin, and AHP. The dissociation constant for the aldehyde-enzyme complex is so small that it has been possible to estimate an upper limit of the number of equivalents of enzyme present.