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 Inagaki, C. Articles by Schwartz, A. Search for Related Content PubMed PubMed Citation Articles by Inagaki, C. Articles by Schwartz, A. Social Bookmarking                      What's this?

Effects of Sodium and Potassium on Binding of Ouabain to the Transport Adenosine Triphosphatase

From the ¹ From the Departments of Cell Biophysics and Medicine, Division of Myocardial Biology, Baylor College of Medicine, and the Fondren-Brown Cardiovascular Research and Training Center of the Methodist Hospital, Houston, Texas 77025

The effects of sodium and potassium on the rate of ouabain binding to sodium and potassium ion-activated adenosine triphosphatase, isolated from the outer medulla of canine kidney, were examined in the presence of a magnesium ATP complex (37°; pH 7.4). In the presence of high sodium ( 10 mm), sodium accelerated and potassium retarded the rate of binding through a process kinetically defined by competition between sodium and potassium for a common site. The slow rate of binding in the presence of magnesium·ATP was also elevated by low sodium and retarded by potassium. The sensitivity of the latter reaction to potassium appeared to be an inverse function of the magnesium·ATP concentration and the ability of potassium to inhibit ouabain binding in the absence of sodium correlated with its ability to inhibit a ouabain-sensitive, magnesium-dependent ATPase activity, which was observed in the absence of sodium. These findings are consistent with glycoside binding to a receptor conformation that exist within the enzyme turnover cycle, which can operate under three conditions: high sodium and high potassium = fast rate; low sodium and zero potassium = intermediate rate; zero sodium and zero potassium = very slow rate. The antagonism between magnesium·ATP and potassium may reflect conversion of the enzyme from one state to another by magnesium·ATP which counteracts a potassium-induced stabilization of the other state. The kinetic data are also consistent with the existence of two sodium-dependent glycoside binding sites. If the latter were the case, analysis of the reaction rates at varying concentrations of sodium suggested two apparent "sites" for sodium-enzyme interaction, one with K_a of 16 mm and the other with K_a of 0.63 mm.

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				H. Schneider and G. Scheiner-Bobis Involvement of the M7/M8 Extracellular Loop of the Sodium Pump alpha  Subunit in Ion Transport. STRUCTURAL AND FUNCTIONAL HOMOLOGY TO P-LOOPS OF ION CHANNELS J. Biol. Chem., June 27, 1997; 272(26): 16158 - 16165. [Abstract] [Full Text] [PDF]

				Y. Wang, K. A. Lindstedt, and P. T. Kovanen Mast Cell Granule Remnants Carry LDL Into Smooth Muscle Cells of the Synthetic Phenotype and Induce Their Conversion Into Foam Cells Arterioscler. Thromb. Vasc. Biol., June 1, 1995; 15(6): 801 - 810. [Abstract] [Full Text]