Effects of barium on gastric microsomal K+-stimulated para-nitrophenyl phosphatase activity.
Ba2+ at low concentrations (1 mM or lower) stimulates the basal and K+-stimulated para-nitrophenyl phosphatase activity associated with the purified microsomal fractions from the oxyntic cells of bullfrog gastric mucosa. However, at higher concentrations Ba2+ acts as a competitive inhibitor of the K+-stimulated phosphatase. Ba2+ alone, in absence of any Mg2+, cannot maintain the enzyme activity; hence Ba2+ can only influence or modulate the Mg2+-dependent phosphatase. The effects are unique for Ba2+ because all other divalent cations such as Ca2+ and Zn2+ act as inhibitors of this enzyme under similar conditions. The data offer a possible biochemical basis for the known pharmacological effects of Ba2+ in gastric acid secretion.
D009597:4-Nitrophenylphosphatase / Q000378:metabolism*; D000818:Animals; D001464:Barium / Q000494:pharmacology*; D066298:In Vitro Techniques; D008861:Microsomes / Q000201:enzymology*; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D011892:Rana catesbeiana; D013270:Stomach / Q000201:enzymology*
D001464:Barium; D010744:Phosphoric Monoester Hydrolases; D009597:4-Nitrophenylphosphatase; D011188:Potassium