title: Labeling of a thiol residue in sarcoplasmic reticulum ATPase by pyrene maleimide. Solvent accessibility studied by fluorescence quenching.
abstract: Sarcoplasmic reticulum ATPase was specifically labeled by the fluorescent probe N-(1-pyrene)maleimide which modified 1 mol of a highly reactive thiol residue per mol of ATPase under appropriate conditions, when the probe concentration was varied in the range 0.1-1.5 microM. Addition of inorganic phosphate to the labeling medium increased both the rate of labeling and the number of modified thiol residues. Addition of ATP gave a marked kinetic protection from labeling, suggesting that the label was attached to a protein domain which is sensitive to changes at the catalytic site. Quenching of pyrene fluorescence emission of labeled ATPase by acrylamide and cesium chloride gave linear Stern-Volmer plots. The Stern-Volmer quenching constants of pyrene-ATPase fluorescence were 10 times lower than the constant obtained for acrylamide quenching of the fluorescent adduct of pyrene-maleimide-cystein used as a control, indicating that the pyrene moiety of the probe was considerably shielded from the medium solvent when covalently attached to the ATPase. The efficiency of quenching of pyrene-ATPase fluorescence increased by a significant amount upon addition of 100 microM Ca2+, when compared to the quenching in the presence of a Ca2+ chelator. It suggests that occupancy of the high affinity Ca2+ sites of the ATPase increases the accessibility of medium solvent into hydrophobic domains of the enzyme. The fluorescence lifetime of the solubilized pyrene-ATPase emission was 144-149 ns. The fluorescence polarization of pyrene-ATPase solubilized by nonionic detergent C12E8 was rho = 0.10 and it increased with an increase in the viscosity of the medium yielding a linear Perrin plot. The rotational correlation time for the soluble ATPase was 532 ns, corresponding to the overall rotation of a detergent-pyrene-ATPase particle with radius of 87A.
authors.forename: E
authors.initials: E
authors.lastname: Kurtenbach
authors.forename: S
authors.initials: S
authors.lastname: Verjovski-Almeida
mesh_terms: D020106:Acrylamide; D000178:Acrylamides; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002586:Cesium; D002712:Chlorides; D005454:Fluorescence Polarization; D005456:Fluorescent Dyes / Q000378:metabolism*; D007700:Kinetics; D008301:Maleimides / Q000378:metabolism*; D008433:Mathematics; D009132:Muscles / Q000201:enzymology*; D010766:Phosphorylation; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D012997:Solvents
chemical_list: D000178:Acrylamides; D002712:Chlorides; D005456:Fluorescent Dyes; D008301:Maleimides; D012997:Solvents; D002586:Cesium; D020106:Acrylamide; D000255:Adenosine Triphosphate; C003944:N-(3-pyrene)maleimide; D000251:Adenosine Triphosphatases; C028019:cesium chloride; D002118:Calcium