title: Mutational analysis of the role of Glu309 in the sarcoplasmic reticulum Ca(2+)-ATPase of frog skeletal muscle.
abstract: Site-specific mutagenesis was used to analyse the role of the residue, Glu309, in the function of the Ca(2+)-ATPase of frog skeletal muscle sarcoplasmic reticulum by substitution with Ala or Lys. At pH 6.0, 100 microM Ca2+ was unable to prevent phosphorylation from Pi, consistent with previous observations on the Ca(2+)-ATPase of rabbit fast twitch muscle [Clarke, D.M., Loo, T.W, Inesi, G. and MacLennan, D.H. (1989) Nature 339, 476-478]. At neutral pH, however, micromolar concentrations of Ca2+ were sufficient to inhibit phosphorylation of the Glu309----Lys mutant from inorganic phosphate, suggesting that at least one high-affinity Ca2+ site was relatively intact in this mutant. The Glu309----Lys mutant was unable to form a phosphoenzyme from ATP at all Ca2+ concentrations studied (up to 12.5 mM), whereas phosphorylation of the Glu309----Ala mutant occurred at 12.5 mM Ca2+, but not at Ca2+ concentrations in the submillimolar range. Kinetic studies demonstrated a reduced rate of dephosphorylation of the E2P intermediate in the Glu309----Lys mutant. A less pronounced stabilization of E2P was observed with the Glu309----Ala mutant, suggesting a possible role of the charge at the position of Glu309 in phosphoenzyme hydrolysis.
authors.affiliation: Danish Biomembrane Research Centre, University of Aarhus, Denmark.
authors.forename: B
authors.initials: B
authors.lastname: Vilsen
authors.forename: J P
authors.initials: JP
authors.lastname: Andersen
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001001:Anura; D000252:Calcium-Transporting ATPases / Q000235:genetics / Q000378:metabolism*; D002461:Cell Line, Transformed; D004594:Electrophysiology; D005973:Glutamine / Q000502:physiology*; D009154:Mutation; D010766:Phosphorylation; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*
chemical_list: D005973:Glutamine; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases