Isomerization of 6-lactoyl tetrahydropterin by sepiapterin reductase.

Isomerization of 6-1'-oxo-2'-hydroxypropyl tetrahydropterin (6-lactoyl tetrahydropterin) to 6-1'-hydroxy-2'-oxopropyl tetrahydropterin has been attributed to sepiapterin reductase. The activity is N-acetylserotonin-insensitive and has a well defined pH optimum of 8.6. The product of the reaction was detected on a HPLC chromatogram by means of electrochemical oxidation at 200 mV according to Smith and Nichol (J. Biol. Chem. 261, 2725-2737 (1986]. The C2'-keto structure of the product was confirmed by 1H-NMR spectroscopy.