Purification and Properties of l‐6‐Hydroxynicotine Oxidase

l ‐6‐Hydroxynicotine oxidase, an inducible enzyme of nicotine catabolism in Arthrobacter oxidans , was obtained as a homogeneous protein, as judged by electrophoresis and ultracentrifuge studies; it forms hexagonal crystals in ammonium sulfate solution. Its molecular weight was determined to be 93,000. It contains two moles of FAD per mole of enzyme. In the presence of guanidine hydrochloride, enzymatically inactive components of molecular weight 47,000 were formed which appear to represent the subunits of the protein. No evidence for a participation of metal ions in the electron transport of the enzyme was obtained. Although Hg 2+ and p ‐chloromercuriphenylsulfonate strongly affect activity, N ‐ethylmaleimide and 5,5′‐dithiobis‐(2‐nitrobenzoate) do not inhibit the enzyme. The latter compound reacts with one thiol group only after exposure of the enzyme to 7.5 M urea.