ACT domain of the nonheme iron-dependent aromatic amino acid hydroxylase, phenylalanine hydroxylases (PAH)
ACT domain of the nonheme iron-dependent aromatic amino acid hydroxylase, phenylalanine hydroxylases (PAH). PAH catalyzes the hydroxylation of L-Phe to L-Tyr, the first step in the catabolic degradation of L-Phe. In PAH, an autoregulatory sequence, N-terminal of the ACT domain, extends across the catalytic domain active site and regulates the enzyme by intrasteric regulation. It appears that the activation by L-Phe induces a conformational change that converts the enzyme to a high-affinity and high-activity state. Modulation of activity is achieved through inhibition by BH4 and activation by phosphorylation of serine residues of the autoregulatory region. The molecular basis for the cooperative activation process is not fully understood yet. Members of this CD belong to the superfamily of ACT regulatory domains.