P. Fitzpatrick
Dec 9, 2003
Citations
9
Influential Citations
241
Citations
Quality indicators
Journal
Biochemistry
Abstract
Phenylalanine hydroxylase (PheH), 1 tyrosine hydroxylase (TyrH), and tryptophan hydroxylase (TrpH) make up the family of tetrahydropterin dependent aromatic amino acid hydroxylases. Scheme 1 illustrates the general reaction these enzymes catalyze, the hydroxylation of the side chain of an aromatic amino acid utilizing a tetrahydropterin as the source of the two electrons required to reduce the other atom of oxygen to the level of water. The eukaryotic forms of these enzymes have been studied the most due to their physiological importance. PheH is a liver enzyme that catalyzes the catabolism of excess phenylalanine in the diet to tyrosine; the vast majority of cases of phenylketonuria are due to deficiencies in this enzyme (1). TyrH is found in the central nervous system and adrenal gland, where its role is to catalyze the first step in the biosynthesis of catecholamines, the formation of dihydroxyphenylalanine (DOPA) from tyrosine. TrpH is present in the brain where it catalyzes the first step in the biosynthesis of serotonin, the hydroxylation of tryptophan to 5-hydroxytryptophan. PheH is also present in bacteria, although not in Escherichia coli ; as of this writing, 17 different bacterial genomes include a PheH ortholog. Only the enzyme from Chromabacterium violaceum has been characterized to any extent. catalyze tetrahydropterin oxidation