The calcium ATPase of sarcoplasmic reticulum is inhibited by one Ca2+ ion

AbstractInhibition by calcium of the steady-state turnover of the calcium ATPase from sarcoplasmic reticulum of rabbit muscle follows a Hill slope of 0.8 ± 0.2 (pH 7.0, 0.1 M KCl, varying [Mg2+] and 2 μM A23187 ionophore). It is concluded that dissociation of the two Ca2+ ions from E-P·Ca2 is sequential and that the inhibition arises from the binding of one Ca2+ to A-P·Ca1