Purification and Characterization of the Secreted Alkaline Phosphatase of Bacillus licheniformis MC14: Identification of a Possible Precursor

Department of Biological Sciences, Laboratory for Cell, Molecular and Developmental Biology, University of Illinois at Chicago, PO Box 4348, Chicago, Illinois 60680, USA ABSTRACT The most abundantly secreted protein from Bacillus licheniformis MC14 is alkaline phosphatase (APase). A twofold purification yields a homogeneous enzyme. No discernible chemical-physical differences in the secreted APase distinguish this enzyme from the cell-bound APase(s) except a 10-fold higher specific activity. During the growth phase in which the bacterium was secreting APase into the medium an inactive cytosol protein antigenically similar but 3000 Da heavier than the subunit of the mature secreted APase was immunoprecipitated from the cytosol. A pulse-chase experiment showed the kinetics of disappearance of this protein from the cytosol to be correlated with the appearance of the secreted APase in the medium, suggesting that it may be a precursor to the secreted APase.