title: A continuous spectrophotometric assay for simultaneous measurement of calcium uptake and ATP hydrolysis in sarcoplasmic reticulum.
abstract: A continuous, spectrophotometric assay to simultaneously measure Ca uptake and ATP hydrolysis has been developed, in order to assess the function of the Ca-ATPase in skeletal and cardiac sarcoplasmic reticulum (SR) vesicles. The absorbance of Fura Red was measured continuously at 490 nm, in EGTA-buffered solutions containing initial free ionized calcium concentrations of 300 nM, 500 nM, 790 nM, and 2 microM, during assays of oxalate-facilitated or phosphate-facilitated active calcium uptake in skeletal SR. Simultaneous measurement of ATP hydrolysis during the measurement of phosphate-facilitated Ca uptake was accomplished by measuring the disappearance of NADH at 340 nm, coupled to the hydrolysis of ATP by an enzyme-linked, continuous ATPase assay. This new method, unlike the standard 45Ca-filtration assay, measures calcium uptake in real time and eliminates the need for radioactivity. Moreover, the rates of calcium uptake and ATP hydrolysis are measured simultaneously, allowing the direct quantitative comparison of the two parameters. This assay will facilitate the characterization of Ca-ATPase function and malfunction in skeletal and cardiac SR and advances the methodology for comparison of normal and physically, chemically, or biologically altered Ca-ATPase.
authors.affiliation: Department of Biochemistry, University of Minnesota Medical School, Minneapolis 55455, USA.
authors.forename: B S
authors.initials: BS
authors.lastname: Karon
authors.forename: E R
authors.initials: ER
authors.lastname: Nissen
authors.forename: J
authors.initials: J
authors.lastname: Voss
authors.forename: D D
authors.initials: DD
authors.lastname: Thomas
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001572:Benzofurans; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000032:analysis*; D005456:Fluorescent Dyes; D006868:Hydrolysis; D007093:Imidazoles; D018482:Muscle, Skeletal / Q000201:enzymology / Q000648:ultrastructure; D009206:Myocardium / Q000201:enzymology / Q000648:ultrastructure; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D013053:Spectrophotometry / Q000379:methods*
chemical_list: D001572:Benzofurans; D005456:Fluorescent Dyes; D007093:Imidazoles; C082877:fura red; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D002118:Calcium