DEVELOPMENTAL-CHANGES IN PTERIDINE BIOSYNTHESIS IN THE TOAD, BUFO-VULGARIS

The presence of blue-violet fluorescent pteridines, neopterin, biopter in, pterin and isoxanthopterin, in a toad tadpole in the various devel opment stages was determined by HPLC with fluorimetric detection. Chan ges in the activities of pteridine- synthesizing enzymes, GTP cyclohyd rolase I, 6-pyruvoyl-tetrahydropterin synthase and sepiapterin reducta se, were also investigated. In contrast to an older report by Hama, ne opterin was already found in the tadpole larval stage, as well as in t he young adult stage. Also, biopterin was found not only in the tadpol e larval stage but also in the young adult stage. Neopterin constitute s the major portion of the pteridines of the animal and biopterin make s up the minor one throughout the whole development stage. In spite of the high content level of neopterin in the young adult stage, the act ivity of GTP cyclohydrolase I, which produces dihydroneopterin triphos phate, declined; and the activity of 6-pyruvoyl-tetrahydropterin synth ase, which metabolizes dihydroneopterin triphosphate as a substrate, r ose in the same stage.