Characterization of (Mg,Ca)-ATPase activity in rat pancreatic plasma membranes.
1. Pancreatic plasma membranes containing a high adenylate cyclase activity and a low contamination by cytochrome c oxidase were isolated from the rat by sucrose density centrifugation. The preparation contained an (Mg,Ca)-ATPase of high activity with the following characteristics. 2. The ATPase activity was shown to have two apparent Km values for Mg-ATP (0.24 +/- 0.09 mM and 1.15 +/- 0.21 mM) and two apparent Km values for Ca-ATP (0.14 +/- 0.09 mM and 0.68 +/- 0.10 mM). Mg-GTP and Ca-GTP were also hydrolysed by the preparation. The phase transition temperature was 19.3 +/- 1.0 degrees C for the Mg-ATPase and 22.6 +/- 1.1 degrees C for the Ca-ATPase activities. 3. Three lines of evidence suggest that Mg-ATP and Ca-ATP were substrates for the same enzyme: Mg-dependent and Ca-dependent activities were not additive; the two activities showed the same pH optimum at 8.0; and the nonionic detergents Triton X-100, Triton X-305, Triton N-101, Lubrol P 12 A, and digitonin, produced a parallel solubilization of the two activities. 4. Enzyme activities were insensitive to potassium, sodium, ouabain, pancreozymin, carbamoyl-choline, secretin, concanavalin A, wheat germ agglutinin, and soybean lectin.
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002458:Cell Fractionation; D002462:Cell Membrane / Q000201:enzymology / Q000648:ultrastructure; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D010179:Pancreas / Q000201:enzymology*; D011092:Polyethylene Glycols / Q000494:pharmacology; D051381:Rats; D013501:Surface-Active Agents / Q000494:pharmacology
D013501:Surface-Active Agents; D011092:Polyethylene Glycols; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D002118:Calcium