Biosynthesis of biopterin in Ascaris lumbricoides suum

In in vivo experiments, radioactivity from [U-14C]GTP was incorporated into biopterin, and, in fact, all carbon atoms of biopterin synthesized in Ascaris lumbricoides suum originated from GTP. Biopterin was also biosynthesized in homogenates of tissue fluid and muscles of Ascaris lumbricoides suum. The enzyme which catalyzes sepiapterin synthesis from D-erythro-7,8-dihydroneopterin-3'-phosphate was found in A. lumbricoides suum extracts and extracted in the 0--30% (NH4)2SO4 fraction from a 40 000 x g supernatant. The enzyme was purified by Sephadex G-200 column and DEAE-cellulose column chromatography. It is suggested that sepiapterin could be an intermediate compound in biopterin biosynthesis.