title: Characterization of microsomal ATPases from developing human placenta.
abstract: Activities and some properties of microsomal ATPases have been studied in developing human placenta. The enzyme activities (Na+ + K+ + Mg2+, Mg2+, and Ca2+ dependent) in the placenta increase steadily with gestational age until the 18th to 21st week, and decrease in the second half of pregnancy. Mg2+-dependent and Na+ + K+ + Mg2+-dependent ATPases possess nearly the same Km (apparent) for ATP, while the Ca2+-dependent enzyme shows a different one. Mg2+-dependent ATPase shows higher substrate affinity than Ca2+-dependent ATPase, although the Vmax of the Mg2+-dependent enzyme is lower than that of the latter. However, for each enzyme, the Km remains almost constant and Vmax varies during ontogenic development. Vmax of the enzymes decline at term. The enzymes are heat-labile, unaffected by amino acids, namely, L-phenylalanine, L-leucine, and L-tryptophan, and deoxycholate inhibits the enzyme activities by about 50%.
mesh_terms: D000251:Adenosine Triphosphatases / Q000302:isolation & purification* / Q000378:metabolism; D017301:Ca(2+) Mg(2+)-ATPase / Q000302:isolation & purification; D000252:Calcium-Transporting ATPases / Q000302:isolation & purification; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D005260:Female; D005865:Gestational Age; D006801:Humans; D007700:Kinetics; D008861:Microsomes / Q000201:enzymology*; D010920:Placenta / Q000648:ultrastructure*; D011247:Pregnancy; D000254:Sodium-Potassium-Exchanging ATPase / Q000302:isolation & purification
chemical_list: D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase