Dihydrobiopterin reductase activity is needed to replenish quinonoid-dihydrobiopterin back into its tetrahydrobiopterin form, which is an important cofactor in many reactions in amino acid metabolism.
2.
The pterin cofactor is regenerated by hydration of the carbinolamine product of PAH to quinonoid dihydrobiopterin ( qBH 2 ), which is then reduced to BH 4.
3.
This mechanism is supported by mutations of Arg219 . Mutations changing Arg219 to a carboxylate result in a quinonoid intermediate being detected whereas none was detected with arginine.
4.
A substance that it secretes, 2, 3-dimethoxy-geranyl-1, 4-benzoquinone ( consisting of a quinonoid ring with a 10 or 11 carbon-membered side chain ) is a remarkably strong sensitizer, which is found nowhere else in the plant kingdom.
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