The phosphate regulation and subcellular location of the hydrolytic enzyme alkaline phosphatase were investigated in the Gram-negative bacterium . The biosynthesis of alkaline phosphatase was not derepressed at a low phosphate concentration as is generally observed in other micro-organisms, nor was it repressed by high phosphate concentrations in the medium. The enzyme level was rather constant during the growth phases in batch culture, at a value at least 8.4-fold lower than that observed in . The alkaline phosphatase of was found associated with the membrane fraction after cell disruption, osmotic shock treatment or spheroplast formation. This is a rather unusual location, since most of the alkaline phosphatases from Gram-negative bacteria have been shown to be periplasmic enzymes. Activity staining on polyacrylamide gels after two-dimensional electrophoresis revealed two isoforms of alkaline phosphatase, each of approximate molecular mass 56 kDa. These two forms belong to a group including the more basic envelope proteins of . Our results indicate that the enzyme from differs markedly from typical alkaline phosphatases of other Gram-negative bacteria.


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