Tryptophan side chain oxidase from Pseudomonas. Oxidation of skatole to indole-3-carboxaldehyde via indole-3-methanol.

Tryptophanside chain oxidase from Pseudomonas was shown to catalyze two consecutive oxidations in which skatole was first oxidized to indole-3-methanol, and then to indole-3-carboxaldehyde;indole-3-metha-no1 was the reaction product of skatole and also a substrate for the enzyme.A half-equivalent of oxygen was consumed for each reaction.The reaction also proceeded under anaerobic conditions with ferricyanide as an electron acceptor.Two equivalents of ferricyanide were reduced for each reaction.Both reactions were assayed spectrophotometrically at a constant oxygen concentration (air-saturated buffer) at 25°C.Hyperbolic substrate saturation curves were obtained with both skatole and indole-3-methanol.The K, values for skatole and indole-3-methanol were 15.4 and 43.5 pM, respectively, at pH 6.0.The ratio of the V,, for skatole to indole-3-methanol was 0.88.Each substrate inhibited the oxidation of the other.The apparent Ki values for skatole and indole-3-methanol were 16.7 and 44.1 m, respectively.These results indicated that both reactions were catalyzed by a single enzyme.The reactions at various concentrations of oxygen were performed at a fixed concentration of the substrate, 0.2 mu skatole or 0.5 mu indole-3-methanol; the apparent K,,, values for oxygen were 50 and 55 PM, respectively.The substrate specificity of the enzyme was analyzed with special reference to l-and 2-substituted skatole derivatives.The activity to 2,3-dimethylindole (0.5 mu) was one-half of that to skatole (0.5 111~).Neither lacetyl nor l-methyl derivatives could serve as substrate or inhibitor for the enzyme.