title: Purification and partial characterization of the I variant of placental alkaline phosphatase.
abstract: The I variant of placental alkaline phosphatase was purified to homogeneity by means of DEAE-cellulose chromatography, isoelectric focusing, and gel filtration on AcA-34. The specific activity of the I variant was found to be 3.33 micronkat/mg. The enzyme is a dimer with an isoelectric point of 4.6 and a molecular weight of 120,000 as determined by sodium dodecylsulfate electrophoresis. The amino acid composition and other physiocochemical properties of the I variant were compared with those of the more common F and S variants. The low activity associated with the I variant is apparently not due to a low specific activity, but to decreased molecular stability. The behavior in the ultracentrifuge and other observations suggest that the I variant differs from the F and S variants in surface charge distribution.
mesh_terms: D000469:Alkaline Phosphatase / Q000032:analysis / Q000302:isolation & purification*; D000596:Amino Acids / Q000032:analysis; D005260:Female; D014644:Genetic Variation; D006801:Humans; D010920:Placenta / Q000201:enzymology*; D011247:Pregnancy
chemical_list: D000596:Amino Acids; D000469:Alkaline Phosphatase