(1) Cell-free enzyme preparation which catalyzes an oxidative breakdown of gentisic acid with rupturing of benzene ring was obtained from m-hydroxybenzoic acid induced cells of Pseudomonas oxalis S-5. This new benzene ring splitting enzyme was named “Gentisic acid oxidase”
(2) Comparisons of various methods to obtain a cell free enzyme preparation were made. The enzyme was partially purified, and ferrous ion was proved necessary, for the activity of this enzyme. Further, some other properties of the gentisic acid oxidase were also investigated.
(3) From the various evidences obtained by manometrical experiments and chemical reaction of the product of this enzyme, the oxidative pathway of gentisic acid by Ps. ovalis was r presumed to be as follows.

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