Purification and characterization of the 4-hydroxyphenylacetic acid-3-hydroxylase from Pseudomonas putida U

4-Hydroxyphenylacetic acid-3-hydroxylase from Pseudomonas putida U was purified to homogeneity (96-fold) from bacterial cultures grown in a chemically defined medium containing 4-hydroxyphenylacetic acid as the sole carbon source. The maximal rate of catalysis occurred at pH 7.5 and 40°C. Under these conditions, the K_m values calculated for 4-hydroxyphenylacetic acid, NADH and FAD were 38, 41 and 4 μM respectively. The native enzyme (M_r 65 000) had two identical subunits in an α₂ oligomeric structure and required the addition of FAD, so it was classified as an external flavoprotein monooxygenase. 4-Hydroxyphenylacetic acid-3-hydroxylase showed a broad substrate range. It was specifically induced by 4-hydroxyphenylacetic acid, although phenylacetic acid and some phenyl-alkanoic acids also induced enzymatic activity to a lesser extent. 4-Hydroxyphenylacetic acid-3-hydroxylase induction and 4-hydroxyphenylacetic acid consumption were unaffected by the presence of glucose, suggesting that the uptake and hydroxylation of 4-hydroxyphenylacetic acid are not under carbon catabolite repression.