Accumulated BH4 in mouse liver caused by administration of either 6R- or 6SBH4 consisted solely of the 6R-diastereomer: evidence of oxidation to BH2 and enzymic reduction.

Abstract Mice were given (i.p.) L- erythro -(6S)-tetrahydrobiopterin (6SBH 4 ) or 6RBH 4 and the increase in liver BH 4 in both groups was almost the same. The C6-chirality of liver BH 4 was determined by HPLC. After administration of 6SBH 4 , the liver BH 4 consisted mainly of 6RBH 4 (>95%). These findings show that the exogenous BH 4 was oxidized to 7,8BH 2 which was then taken up and enzymically reduced back to BH 4 in the liver.