ABSTRACT
A membrane-associated, Ca2+-activated, Mg2+-dependent ATPase activity has been identified in the mouse chorioallantoic placenta. The enzyme activity is expressed and increases as a function of gestation. Bio-chemical characterization shows that the enzyme is highly specific for Ca2+ and nucleotide triphosphates, with a Km of 0.97 mM [Ca2+] and a Vmax of 1.05 nmol Pt released mg-1 placental protein min-1. The mouse placental Ca2+-ATPase activity has a pl of approximately 6.8, and corresponds to two apparent Mr values of 118 and ISOxlO3, based on Ferguson analysis of non-denaturing electrophoretograms. Enzyme activity is inhibited by phenothiazin (suggesting a calmodulin dependence), vanadate, erythrosin B and quercetin, but not by ouabain or levamisole. Enzyme cytohistochemistry revealed that the Ca2+-ATPase is localized to’polyploid trophoblastic cells of the mouse inner placenta. These results suggest that the enzyme may be a functional component of transplacental calcium transport during mouse embryonic development.