HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Dixon, D. A. Articles by Haynes, D. H. Search for Related Content PubMed PubMed Citation Articles by Dixon, D. A. Articles by Haynes, D. H. Social Bookmarking                      What's this?

J. Biol. Chem., Vol. 264, Issue 23, 13612-13622, 08, 1989

Kinetic characterization of the Ca2+-pumping ATPase of cardia sarcolemma in four states of activation

DA Dixon and DH Haynes
Department of Pharmacology, University of Miami School of Medicine, Florida 33101.

The Ca2+ dependence of the Ca2+-pumping ATPase of bovine cardiac sarcolemma was studied for four states of activation: (a) unactivated, (b) cAMP-dependent protein kinase (cAMP protein kinase C-subunit)- activated, (c) calmodulin (CAM)-activated, and (d) CAM plus cAMP protein kinase C-subunit-activated. Analysis of the Ca2+ dependence of active transport gave the following Vmax (nanomoles Ca2+/(mg x min], Km (nM) for Ca2+, and Hill coefficient values for the four states at pH 7.4, 37 degrees C: (a) 1.7 +/- 0.3, 1800 +/- 100, 1.6 +/- 0.1; (b) 3.1 +/- 0.5, 1100 +/- 100, 1.7 +/- 0.1; (c) 15.0 +/- 2.5, 64 +/- 1.4, 3.7 +/- 0.2; and (d) 36.0 +/- 6.5, 63 +/- 1.7, 3.7 +/- 0.1. CAM has the most dramatic effect, increasing the apparent Ca2+ affinity by a factor of 28, increasing the Hill coefficient 2.0 units to a value approaching 4 and increasing the Vmax by a factor of 9 or 12. The effective Ca2+ concentration (EC50) for the Ca2+-induced activation of the enzyme in the presence of 5 microM calmodulin is close to the Km for Ca2+ for the CAM-activated state (64 nM). Activation by cAMP protein kinase C- subunit had only minor effects on the Km and Hill coefficient, but increased the Vmax of both the unactivated and the CAM-activated forms of the pump by factor of 1.8 and 2.4, respectively. Analysis suggests that CAM activation is the result of direct binding of Ca2-CAM or high complexes, conferring higher Ca2+ affinity to the enzyme. Analysis suggests that regulatory phosphorylation (cAMP protein kinase C- subunit) increases the rates of processes subsequent to or distinct from Ca2+ binding. The CAM-activated form of the pump was further characterized. Unexpectedly, this form of the enzyme is stimulated a factor of 1.9 by ADP, with half-maximal stimulation between 0.4 and 0.7 mM. Analysis of the progress curves for uptake show that the CAM- activated enzyme is highly resistant to inhibition by transported Ca2+, with an IC50 of 32 mM. The implications of these findings for the pump mechanism and for its role in the regulation of cardiac contractility are discussed.
CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				A. Takeuchi, S. Tatsumi, N. Sarai, K. Terashima, S. Matsuoka, and A. Noma Ionic Mechanisms of Cardiac Cell Swelling Induced by Blocking Na+/K+ Pump As Revealed by Experiments and Simulation J. Gen. Physiol., November 1, 2006; 128(5): 495 - 507. [Abstract] [Full Text] [PDF]

				H. Reuter, C. Pott, J. I. Goldhaber, S. A. Henderson, K. D. Philipson, and R. H.G. Schwinger Na+-Ca2+exchange in the regulation of cardiac excitation-contraction coupling Cardiovasc Res, August 1, 2005; 67(2): 198 - 207. [Abstract] [Full Text] [PDF]

				J. J. Saucerman, L. L. Brunton, A. P. Michailova, and A. D. McCulloch Modeling {beta}-Adrenergic Control of Cardiac Myocyte Contractility in Silico J. Biol. Chem., November 28, 2003; 278(48): 47997 - 48003. [Abstract] [Full Text] [PDF]

				E. E. Strehler and D. A. Zacharias Role of Alternative Splicing in Generating Isoform Diversity Among Plasma Membrane Calcium Pumps Physiol Rev, January 1, 2001; 81(1): 21 - 50. [Abstract] [Full Text] [PDF]