Purification and properties of p-hydroxybenzoate hydroxylases from Rhodococcus strains

Grain-positive bacteria of the genus Rhodococcus catabolize p-hydroxybenzoa te (PHB) through the initial formation of 3,4-dihydroxybenzoate, High level s of p-hydroxybenzoate hydroxylase (PHBH) activity are induced in six diffe rent Rhodococcus species when these strains are grown on PHB as sole carbon source. The PHBH enzymes were purified to apparent homogeneity and appeare d to be homodimers of about 95 kD with each subunit containing a relatively weakly bound FAD. In contrast to their counterparts from gram-negative mic roorganisms, the Rhodococcus PHBH enzymes prefer NADH to NADPH as external electron donor. All purified enzymes were inhibited by Cl- and for five of six enzymes more pronounced substrate inhibition was, observed in the prese nce of chloride ions.