Protocatechuate 3,4-dioxygenase ( EC 1.13.11.3 ) catalyses the ring cleavage step in catabolism of aromatic compounds through the protocatechuate branch of the β-ketoadipate pathway. The protocatechuate 3,4-dioxygenase was purified to homogeneity from the thermophilic Geobacillus strain grown on naphthalene for the first time. The enzyme was purified about 24-fold with a specific activity of 34.2 U mg of protein^-1 by a purification procedure including ammonium sulfate fractionation and column chromatographies on DEAE–cellulose and hydroxylapatite. The relative molecular mass of the native enzime estimated on gel chromatography of Sephadex G-200 was 480 kDa. The pH and temperature optima for enzyme activity were 8 and 60 ^oC, respectively.
A half-live of the protocatechuate 3,4-dioxygenase at the optimumo temperature was 40 min. The kinetic parameters of the Geobacillus strain protocatehuate 3,4-dioxygenase were determinated. The enzyme gave typical saturation kinetics and had an apparent K_m of 7 µM for protocatechuate and 33 µM for catechol.

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