title: Mechanism of inhibition of the calcium pump of sarcoplasmic reticulum by thapsigargin.
abstract: The steady-state ATPase activity of sarcoplasmic-reticulum (Ca(2+)-Mg2+)-ATPase is inhibited by thapsigargin at a molar ratio of 1:1, with a dissociation constant for thapsigargin estimated to be in the sub-nanomolar range. In the presence of thapsigargin, only a single Ca2+ ion binds to the ATPase. Similarly, addition of thapsigargin to the ATPase incubated in the presence of Ca2+ results in the release of one of the two originally bound Ca2+ ions. As monitored by the fluorescence of nitrobenzo-2-oxa-1,3-diazole-labelled ATPase, thapsigargin appears to shift the transition between E1 and E2 conformations towards E2. Addition of thapsigargin prevents phosphorylation of the ATPase by P(i) and results in a very low steady-state level of phosphorylation of the ATPase by ATP, as observed previously for nonylphenol.
authors.affiliation: Department of Biochemistry, University of Southampton, U.K.
authors.forename: M
authors.initials: M
authors.lastname: Wictome
authors.forename: I
authors.initials: I
authors.lastname: Henderson
authors.forename: A G
authors.initials: AG
authors.lastname: Lee
authors.forename: J M
authors.initials: JM
authors.lastname: East
mesh_terms: D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000037:antagonists & inhibitors* / Q000302:isolation & purification; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors* / Q000302:isolation & purification; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008962:Models, Theoretical; D009132:Muscles / Q000201:enzymology; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D013729:Terpenes / Q000494:pharmacology*; D019284:Thapsigargin; D014638:Vanadates / Q000494:pharmacology
chemical_list: D013729:Terpenes; D014638:Vanadates; D019284:Thapsigargin; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D002118:Calcium