A New Pteridine from Tetrahymena

Ciliapterin, a new unconjugated pteridine, has been isolated from the ciliated protozoan, Tetrahymena pyriformis. It has been determined by alkaline permanganate oxidation to be a 2-amino-4-hydroxy-6-substituted pteridine and by acid hydrolytic treatment to possess no labile bonds (such as glycosidic or phosphoester). The substitution at position 6 is dihydroxypropyl, as shown by the identification of acetaldehyde as one of the products of periodate oxidation. Although its absorbance spectrum is identical with that of biopterin, its fluorescence and activation spectra are similar, but not identical, with those of biopterin. Mobilities on paper with a number of solvent systems and its elution patterns from cation and anion exchange columns together with its biological activity in the Crithidia system indicate that it is 2-amino-4-hydroxy-6-(threo-dihydroxypropyl)pteridine. Its biological activity suggests that it may be the l-threo compound. The origin of this pteridine has been shown, by the use of both guanine-2-14C and uniformly labeled guanosine monophosphate-14C in the culture medium, to be entirely from guanosine. No hydroxymethylpteridine could be detected, indicating the inability of this organism to produce the pteridine precursor of folic acid.