On the relation of heavy metals to the activity and heat stability of alkaline phosphatase from human placenta

Abstract

It is well established that human placentae contain high amounts of alkaline phosphatase (orthophosphoric monoester phosphohydrolase, EC 3.1.3.1) and that the rise in alkaline phosphatase activity in serum during pregnancy is to be ascribed to the presence of this placental enzyme. The placental isoenzyme is characterized by its stability at temperatures up to 65 °C. The enzyme kinetics of alkaline phosphatase extracted from human placentae and its sensitivity to various inhibitors were studied and a search for the divalent cation requirements with respect to activity and heat stability was undertaken. The activity of placental alkaline phosphatase could be abolished by treatment with EDTA. From reactivation studies with different divalent cations it appears that Zn2+ or Mg2+ are necessary for both the activity and the resistance to heat treatment. Hg2+ can replace either of the two former cations in both aspects, albeit to a lesser extent.