Biosynthesis of tetrahydrobiopterin. Purification and characterization of 6-pyruvoyl-tertrahydropterin synthase from human liver

Abstract

6-Pyruvoyl-tetrahydropterin synthase, which catalyzes the first step in the conversion of 7,8-dihydroneopterin triphosphate to tetrahydrobiopterin, was purified approximately 140,000-fold to apparent homogeneity from human liver. The molecular mass of the enzyme is estimated to be 83 kDa. 7,8-Dihydroneopterin triphosphate was a substrate of the enzyme in the presence of Mg²⁺, and the pH optimum of the reaction was 7.5 in Tris HCl buffer. The K_m value for 7,8-dihydroneopterin triphosphate was 10 μM. The product of this enzymatic reaction was the presumed intermediate 6-pyruvoyl-tetrahydropterin. This latter compound was converted to tetrahydrobiopterin in the presence of NADPH and partially purified sepiapterin reductase from human liver. The conditions and the effect of N-acetyserotonin on this reaction, and on the formation of the intermediates 6-(1′-hydroxy-2′-oxopropyl)-tetrahydropterin and 6-(1′oxo-2′-hydroxypropyl)-tetrahydropterin have been studied.