The Isolation and Characterization of Clones of 4a-Hydroxytetrahydrobiopterin Dehydratase

The phenylalanine hydroxylating system is complex, consisting of three enzymes and two coenzymes1,2,3. One of the coenzymes, NADH, plays a near-ubiquitous role in intermediary metabolism. By contrast, the other cofactor, tetrahydrobiopterin (BH4), discovered during our early studies on the characterization of the phenylalanine hydroxylating system,1 plays a unique role as the essential coenzyme for certain hydroxylases such as the enzymes that catalyze the hydroxylation of the aromatic amino acids, phenylalanine, tyrosine and tryptophan3.