NMR spectroscopy and X-ray crystallography have provi-ded important insight into structural features of phenyl-alanine hydroxylase (PAH) and tyrosine hydroxylase (TH). Nevertheless, significant problems such as the substrate specificity of PAHand the different susceptibility of TH to feedback inhibition by L-3,4-dihydroxyphenylalanine (L-DOPA) compared with dopamine (DA) remain unre-solved. Based on the crystal structures 5pah for PAHand 2toh for TH(Protein Data Bank), we have used molecular docking to model the binding of 6(R)-L-erythro-5,6,7,8-tetrahydrobiopterin (BH4) and the substrates phenylalanine and tyrosine to the catalytic domains of PAHand TH
