Relationship between Ca(2+)-transport and ATP hydrolytic activities in guinea-pig pancreatic acinar plasma membranes.
Partially purified plasma membrane fractions were prepared from guinea-pig pancreatic acini. These membrane preparations were found to contain an ATP-dependent Ca(2+)-transporter as well as a heterogenous ATP-hydrolytic activity. The Ca(2+)-transporter showed high affinity for Ca2+ (KCa2+ = 0.04 +/- 0.01 microM), an apparent requirement for Mg2+ and high substrate specificity. The major component of ATPase activity could be stimulated by either Ca2+ or Mg2+ but showed a low affinity for these cations. At low concentrations, Mg2+ appeared to inhibit the Ca(2+)-dependent ATPase activity expressed by these membranes. However, in the presence of high Mg2+ concentration (0.5-1 mM), a high affinity Ca(2+)-dependent ATPase activity was observed (KCa2+ = 0.08 +/- 0.02 microM). The hydrolytic activity showed little specificity towards ATP. Neither the Ca(2+)-transport nor high affinity Ca(2+)-ATPase activity were stimulated by calmodulin. The results demonstrate, in addition to a low affinity Ca2+ (or Mg2+)-ATPase activity, the presence of both a high affinity Ca(2+)-pump and high affinity Ca(2+)-dependent ATPase. However, the high affinity Ca(2+)-ATPase activity does not appear to be the biochemical expression of the Ca(2+)-pump.
Mahey
R
R
Division of Pharmacology and Toxicology, Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, Canada.
Bridges
M A
MA
Katz
S
S
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002147:Calmodulin / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D006168:Guinea Pigs; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D010179:Pancreas / Q000378:metabolism*; D013379:Substrate Specificity
D002147:Calmodulin; D000255:Adenosine Triphosphate; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D002118:Calcium