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Identification of phenylalanine 3-hydroxylase for meta-tyrosine biosynthesis.

Phenylalanine hydroxylase (PheH) is an iron(II)-dependent enzyme that catalyzes the hydroxylation of aromatic amino acid l-phenylalanine (L-Phe) to l-tyrosine (L-Tyr). The enzymatic modification has been demonstrated to be highly regiospecific, forming proteinogenic para-Tyr (p-Tyr) exclusively. Here we biochemically characterized the first example of a phenylalanine 3-hydroxylase (Phe3H) that catalyzes the synthesis of meta-Tyr (m-Tyr) from Phe. Subsequent mutagenesis studies revealed that two residues in the active site of Phe3H (Cys187 and Thr202) contribute to C-3 rather than C-4 hydroxylation of the phenyl ring. This work sets the stage for the mechanistic and structural study of regiospecific control of the substrate hydroxylation by PheH.