Purification and properties of NADH/NADPH-dependent p-hydroxybenzoate hydroxylase from Corynebacterium cyclohexanicum

Crude soluble extracts of Corynebacterium cyclohexanicum, grown on cyclohexanecarboxylic acid, were found to contain 4-hydroxybenzoate 3-hydroxylase which functions with NADH as well as NADPH. The purified enzyme preparation was electrophoretically homogeneous and contained FAD as prosthetic group. The relative molecular mass of the enzyme was estimated to be about 47000 by native and denaturated acrylamide gel electrophoresis, indicating that it is monomeric. The enzyme was stable at 60 degrees C for 10 min. The enzyme was highly specific for p-hydroxybenzoate. The activity was inhibited by several aromatic analogues of p-hydroxybenzoate such as p-aminobenzoate, p-fluorobenzoate, o-hydroxybenzoate, m-hydroxybenzoate, 2,4-dihydroxygenzoate, and 2,5-dihydroxybenzoate. The Km value for NADH was fairly constant, about 45 microM, in the pH range 7.0-8.4, whereas the Km value for NADPH increased from 63 microM to 170 microM as the pH rose from 7.0 to 8.4. V values in the same pH range, however, were approximately constant in both cases; about 30 mumol min-1 mg-1 for NADH, and 26 mumol min-1 mg-1 for NADPH. Mg2+ was required for full activity of the enzyme in low concentrations of phosphate buffer. The enzyme was inhibited by C1- which was non-competitive with respect to NADH, NADPH and p-hydroxybenzoate.