[Relationship of Pseudomonas maltophilia alkaline phosphatase to its membranes]

The localization of alkaline phosphomonoesterase (EC 3.1.3.1) was studied in two Pseudomonas species: P. maltophilia VKM B-591 and P. aeruginosa VKM B-889. The former species is characterized by constitutive synthesis of alkaline phosphatase, and its level is not regulated by orthophosphate in the medium. The enzyme of the latter species is orthophosphate-repressible. The two species differ also in the localization of the enzyme in the cell. Under the conditions of derepression (the absence of inorganic phosphate from the medium), the enzyme of the repressible strain of P. aeruginosa is actively synthesized on the membranes and secreted into the medium. Most of the enzyme activity (80--90%) is found in the cultural broth 4 h after phosphorus starvation. In P. maltophilia, 90% of the synthesized enzyme is found in the membrane fraction irrespective of the incubation time under the same conditions. Apparently, a correlation exists between the regulation of alkaline phosphatase synthesis and the localization of the enzyme. It is likely that in P. aeruginosa, just as in E. coli, alkaline phosphatase is synthesized on polysomes attached to the membrane, with the subsequent translocation of the enzyme to the site of its localization. P. maltophilia appears to have a defect in one of its membrane component responsible for the regulation of the synthesis and the secretion of the enzyme in the cell.