title: Thermal uncoupling of the Ca(2+)-transporting ATPase in sarcoplasmic reticulum. Changes in surface properties of light vesicles.
abstract: It is known that the light fraction of rabbit skeletal muscle sarcoplasmic reticulum vesicles can release Ca2+ from the intravesicular space, although the Ca(2+)-conductive channels are present only in the heavy fraction of sarcoplasmic reticulum vesicles. To study the possible pathways of the Ca2+ leakage from light vesicles we have used a short-term treatment for 4.5 min at 45 degrees C which quickly decreases the efficiency of Ca(2+)-transporting ATPase operation without any visible effects on the hydrolytic activity of the Ca(2+)-ATPase in the membranes. The treatment of the vesicles decreased the negative membrane surface potential created by the Ca(2+)-ATPase. Comparative titration of control and heat-treated preparations of light sarcoplasmic reticulum vesicles by K+, Na+, Mg2+, and Ca2+ revealed clear differences in their surface properties. The short-term heating resulted in release of Ca2+ from the vesicles previously loaded with 45Ca2+, which indicates an increase in passive membrane permeability to Ca2+. Study of Ca(2+)-ATPase protein arrangement in the membrane indicated that the heat treatment induced protein oligomerization and some of the Ca(2+)-ATPase molecules acquired intermolecular and intramolecular covalent bonds. From these data, we have concluded that the changes in the surface and structure properties of the vesicle membranes after the short-term heat treatment were the result of clustering of the Ca(2+)-ATPase molecules. This protein rearrangement may create channels for calcium leakage from light sarcoplasmic reticulum vesicles.
authors.affiliation: Department of Biochemistry and Biophysics, Institute of Experimental Biology of the Estonian Academy of Sciences, Harku.
authors.forename: E
authors.initials: E
authors.lastname: Geimonen
authors.forename: M A
authors.initials: MA
authors.lastname: Batrukova
authors.forename: A M
authors.initials: AM
authors.lastname: Rubtsov
mesh_terms: D000818:Animals; D000252:Calcium-Transporting ATPases / Q000737:chemistry / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008081:Liposomes; D008564:Membrane Potentials; D008970:Molecular Weight; D009132:Muscles / Q000201:enzymology*; D011510:Proteolipids; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D013499:Surface Properties; D013816:Thermodynamics
chemical_list: D008081:Liposomes; D011510:Proteolipids; C020485:proteoliposomes; D000252:Calcium-Transporting ATPases