A KINETIC-MODEL FOR THE CA-2+ + MG-2+-ACTIVATED ATPASE OF SARCOPLASMIC-RETICULUM
A KINETIC-MODEL FOR THE CA-2+ + MG-2+-ACTIVATED ATPASE OF SARCOPLASMIC-RETICULUM
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DOI：
10.1042/bj2370217
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发表时间：
1986-07-01
影响因子：
4.1
通讯作者：
LEE, AG
中科院分区：
文献类型：
--
作者：
GOULD, GW;EAST, JM;LEE, AG
The Ca2+ + Mg2+-activated ATPase of sarcoplasmic reticulum exhibits complex kinetics of activation with respect to ATP. ATPase activity is pH-dependent, with similar pH-activity profiles at high and low concentrations of ATP. Low concentrations of Ca2+ in the micromolar range activate the ATPase, whereas activity is inhibited by Ca2+ at millimolar concentrations. The pH-dependence of this Ca2+ inhibition and the effect of the detergent C12E8 (dodecyl octaethylene glycol monoether) on Ca2+ inhibition are similar to those observed on activation by low concentrations of Ca2+. On the basis of these and other studies we present a kinetic model for the ATPase. The ATPase is postulated to exist in one of two conformations: a conformation (E1) of high affinity for Ca2+ and MgATP and a conformation (E2) of low affinity for Ca2+ and MgATP. Ca2+ binding to E2 and to the phosphorylated form E2P are equal. Proton binding at the Ca2+-binding sites in the E1 and E2 conformations explains the pH-dependence of Ca2+ effects. Binding of MgATP to the phosphorylated intermediate E1''PCa2 and to E2 modulate the rates of the transport step E1''PCa2-E2''PCa2 and the return of the empty Ca2+ sites to the outside surface of the sarcoplasmic reticulum as well as the rate of dephosphorylation of E2P. Only a single binding site for MgATP is postulated.
