A 2.5 Å resolution data set has been collected for crystals of protocatechuate 3,4-dioxygenase from Pseudomonas aeruginosa. Analysis of the data using the rotation function shows that the α2β2 tetramers associate to form a particle with cubic 23 (T) point group symmetry. Prior to this analysis it was believed that eight tetramers associated to form the holoenzyme. The symmetry of the crystalline holoenzyme also addresses questions concerning its iron content and substrate stoichiometry.
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We thank the Genex Corporation, Gaithersburg, MD for use of the Xentronics data collection facility and acknowledge the technical assistance of A. Orville and W. Froland. This work was supported by NIGMS GM24689 to one of us (J.D.L.).