An alkaline phosphatase mutant of Pseudomonas aeruginosa. 1. Effects of regulatory, structural, and environmental shifts on enzyme function.

An alkaline phosphatase mutant of Pseudomonas aeruginosa exhibiting both regulatory and catalytic changes was isolated. Under repression conditions (i.e. high inorganic phosphate (Pi)) the mutant culture produced an alkaline phosphatase (APase) displaying significant activity against both beta-glycerol phosphate (betaGP) and p-nitrophenyl phosphate (pNPP), while the wild type displayed no activity directed towards these substrates under the same conditions. In vivo, the mutant enzyme's ratio of specific activities was 45:1 in favour of betaGP versus pNPP, whereas this ratio was reversed to 1:9 betaGP versus pNPP for the same enzyme isolated from mutant cells. In addition, the kinetic parameters and stability requirements for the mutant-derived enzyme was altered in comparison with those of the wild type. A study of lipopolysaccharide (LPS) preparations from both the mutant and wild type indicated the mutant to be deficient in the core region of its LPS. The authors propose that the modifications in the catalytic activity of the mutant enzyme, demonstrated in vivo, are due to a change in the enzyme's microenvironment.