It has been shown in vivo that patients with the depigmentation disorder
vitiligo accumulate
hydrogen peroxide (H(2)O(2)) accompanied by low
catalase levels and high concentrations of 6- and
7-biopterin in their epidermis. Earlier it was demonstrated that epidermal 4a-OH-tetrahydrobiopterin
dehydratase, an important
enzyme in the recycling process of 6(R)-L-erythro 5,6,7,8
tetrahydrobiopterin (6BH(4)), has extremely low activities in these patients concomitant with a build-up of the abiogenic 7-isomer (7BH(4)), leading to competitive inhibition of epidermal
phenylalanine hydroxylase. A topical substitution for the impaired epidermal
catalase with a
pseudocatalase effectively removes epidermal H(2)O(2), yielding a recovery of epidermal 4a-OH-tetrahydrobiopterin
dehydratase activities and physiologic 7BH(4) levels in association with successful repigmentation demonstrating recovery of the 6BH(4) recycling process. Examination of recombinant
enzyme activities, together with 4a-OH-tetrahydrobiopterin
dehydratase expression in the epidermis of untreated patients, identifies H(2)O(2)-induced inactivation of this
enzyme. These results are in agreement with analysis of genomic
DNA from these patients yielding only wild-type sequences for 4a-OH-tetrahydrobiopterin
dehydratase and therefore ruling out the previously suspected involvement of this gene. Furthermore, our data show for the first time direct H(2)O(2) inactivation of the important 6BH(4) recycling process. Based on this observation, we suggest that H(2)O(2) derived from various sources could be a general mechanism in the regulation of all 6BH(4)-dependent processes.