title: Ca2+- and Mg2+-dependent ATPase activities in the deoxycholate-treated rat heart sarcolemma.
abstract: 1. Isolated rat heart sarcolemma was treated with different concentrations of an ionic detergent, deoxycholate (DOC) and ATP hydrolysis in the presence of Ca2+ or Mg2+ was determined. 2. Both Ca2+-dependent ATPase and Mg2+-dependent ATPase activities were decreased in the DOC-treated membranes; however, the depression of Mg2+-dependent ATPase activity was greater than that of Ca2+-dependent ATPase. 3. The differential changes in Ca2+-dependent ATPase and Mg2+-dependent ATPase activities were apparent when incubations with DOC were carried out for different time intervals and at different temperatures. 4. In DOC-treated preparations, the Km value for Ca2+-dependent ATPase was decreased whereas that for Mg2+-dependent ATPase was increased. The half maximal velocities of the Ca2+-dependent ATPase and Mg2+-dependent ATPase enzyme reactions in the treated preparations were obtained at a DOC: membrane protein ratio of 3.0 and 0.6, respectively. 5. In the DOC-treated membranes exhibiting the half maximal velocities of enzyme reactions, the Ka value for Ca2+-dependent ATPase was drastically reduced but remained unchanged for Mg2+-dependent ATPase. 6. The DOC treatment was associated with a loss of protein as well phospholipids and resulted in changes in the ultrastructural integrity of the membrane. 7. Varying degrees of decreases in the activities of sarcolemmal adenylate cyclase. (Na+-K+)-ATPase, 5'-nucleotidase and calcium binding were seen upon DOC treatment. 8. The extent of reduction in Ca2+-dependent ATPase and Mg2+-dependent ATPase activities were also different when the membrane was treated with a non-ionic detergent, Lubrol PX. 9. These data suggest that Ca2+-dependent ATPase in heart sarcolemma is more resistant than Mg2+-dependent ATPase to detergent treatments and further indicate some differences in the properties of these enzymes.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology; D003840:Deoxycholic Acid / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D008563:Membrane Lipids / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D009206:Myocardium / Q000201:enzymology*; D051381:Rats; D011919:Rats, Inbred Strains; D012508:Sarcolemma / Q000201:enzymology*
chemical_list: D008563:Membrane Lipids; D008565:Membrane Proteins; D003840:Deoxycholic Acid; D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases