Purification and properties of the phosphate eliminating enzyme involved in the biosynthesis of BH4 in man.

An enzyme catalyzing the elimination of triphosphate from 7,8-dihydroneopterin triphosphate in the presence of Mg2+ has been purified approx. 3000 fold from human liver. It has a molecular weight of approx. 63'000, a pI value of 4.4 - 4.6 and is stable at 80 degrees C for 5 min. This enzyme catalyzes the formation of tetrahydrobiopterin in the presence of sepiapterin reductase, Mg2+ and NADPH. It is thus possible, that it also catalyzes the internal oxidoreduction leading to formation of the intermediate 6-pyruvoyl-tetrahydropterin, suggesting that no further enzyme is obligatory for biosynthesis of tetrahydrobiopterin.