1,2-Dihydroxynaphthalene oxygenase was purified from Pseudomonas putida NCIB 9816 grown on naphthalene as the sole source of carbon and energy. The enzyme had a subunit molecular weight of 19,000 and in a medium containing phosphate buffer, 1 mM mercaptoethanol, and 10% (vol/vol) ethanol had a native molecular weight greater than 275,000. The enzyme required Fe2+ for activity. It was inactivate...