17 E. coli Alkaline Phosphatase

This chapter discusses the molecular properties and catalytic properties of E. coli alkaline phosphatase. Purified preparations of alkaline phosphatase from E. coli, judged homogeneous when examined in the analytical ultracentrifuge, contain several isozymes, because several bands which contain enzymic activity are obtained in starch-gel and disc-gel electrophoresis. Although most workers find three brands, four and five equally spaced bands have been found. Single gene mutations apparently affect each isozyme, for the mobility of all the bands are affected without altering the spacing. Levinthal concluded that all of the isozymes were coded for by the same gene. Studies have obtained large single crystals of E. coli alkaline phosphatase. Initial X-ray studies by Hanson show the crystals to be of the space group P3121, each unit cell containing three dimers. The unit cell dimensions are a = 70.5 Å, b = 70.5 Å, c = 155.6 Å, β = 120°, which is consistent with the globular form predicted by the hydrodynamic frictional ratio.