The mature form of l-phenylalanine oxidase (PAOpt) from Pseudomonas sp. P-501 was generated and activated by the proteolytic cleavage of a noncatalytic proenzyme (proPAO). The crystal structures of proPAO, PAOpt, and the PAOpt-o-amino benzoate (AB) complex were determined at 1.7, 1.25, and 1.35A resolutions, respectively. The structure of proPAO suggests that the prosequence peptide of proPAO o...