Phosphate-irrepressible Alkaline Phosphatase of Zymomonas mobilis

Abstract

The phosphate regulation and subcellular location of the hydrolytic enzyme alkaline phosphatase were investigated in the Gram-negative bacterium Zymomonas mobilis. 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 Escherichia coli. The alkaline phosphatase of Z. mobilis 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 Z. mobilis. Our results indicate that the enzyme from Z. mobilis differs markedly from typical alkaline phosphatases of other Gram-negative bacteria.