Evidence for Mg 2+ -Dependent,Na + + K + -Activated ATPase and Ca 2+ -ATPase in the Human Term Placenta 1

Abstract

Summary

Mg²⁺-dependent and Ca²⁺-ATPases were isolated from human term placentas. The Mg²⁺ -dependent ATPase activity was partially inhibited by the absence of Na⁺ or K⁺ from the incubation medium or the presence of ouabain (0.1 mM) or ethacrynic acid (5 mM). This Mg²⁺- dependent, ouabain-sensitive enzyme has a pH optimum near 7.4–7.5, and a substrate specificity for ATP > ITP = GTP. The Mg²⁺ -dependent ATPases were compared with a Ca²⁺-ATPase, which has a pH optimum above 8.0 and was not inhibited by the absence of Na⁺ or K⁺ or the presence of ouabain, but was inhibited by ethacrynic acid.

The investigators gratefully acknowledge the kind assistance of the physicians and nursing staffs from the Obstetrics Departments of the Alice Peck Day Memorial Hospital, Lebanon, NH and the Mary Hitchcock Memorial Hospital, Hanover, NH.