Studies of gastric Ca2+-stimulated adenosine triphosphatase. I. characterization and general properties.
Gastric microsomes do not contain any significant Ca2+-stimulated ATPase activity. Trypsinization of pig gastric microsomes in presence of ATP results in significant (2-3 fold) increase in the basal (with Mg2+ as the only cation) ATPase activity, with virtual elimination of the K+-stimulated component. Such treatment causes unmasking of latent Mg2+-dependent Ca2+-stimulation ATPase. Other divalent cations such as Sr2+, Ba2+, Zn2+, and Mn2+ were found ineffective as a substitute for Ca2+. Moreover, those divalent cations acted as inhibitors of the Ca2+-stimulated ATPase activity. The pH optimum of the enzyme is around 6.8. The enzyme has a Km of 70 microM for ATP and the Ka values for Mg2+ and Ca2+ are about 4 x 10(-4) and 10(-7) M, respectively. Studies with inhibitors suggest the involvement of sulfhydryl and primary amino groups in the operation of the enzyme. Possible roles of the enzyme in gastric H+ transport have been discussed.
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002413:Cations, Divalent / Q000494:pharmacology; D005753:Gastric Mucosa / Q000187:drug effects / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008861:Microsomes / Q000187:drug effects / Q000201:enzymology*; D011188:Potassium / Q000494:pharmacology; D013552:Swine
D002413:Cations, Divalent; D000252:Calcium-Transporting ATPases; D011188:Potassium; D002118:Calcium