Kinetics of Ca2+ binding to the SR Ca-ATPase in the E1 state.

Peinelt, Christine; Apell, Hans-Jürgen (2005). Kinetics of Ca2+ binding to the SR Ca-ATPase in the E1 state. Biophysical journal, 89(4), pp. 2427-2433. Biophysical Society 10.1529/biophysj.105.068411

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The time-resolved kinetics of Ca2+ binding to the SR Ca-ATPase in the E1 state was investigated by Ca(2+)-concentration jump experiments. Ca2+ was released by an ultraviolet-light flash from caged calcium, and charge movements in the membrane domain of the ion pumps were detected by the fluorescent styryl dye 2BITC. The partial reaction (H3E1 <-->) E1 <--> CaE1 <--> Ca2E1 can be characterized by two time constants, tau1 and tau2, both of which are not significantly Ca(2+)-concentration-dependent and only weakly pH-dependent at pH < 7.5. Both time constants differ by a factor of approximately 50 (4.7 vs. 200 ms). The weak substrate-dependence indicates that the rate-limiting process is not related to Ca2+ migration through the access channel and ion binding to the binding sites but to conformational rearrangements preceding the ion movements. The high activation energy obtained for both processes, 42.3 kJ mol(-1) and 60.3 kJ mol(-1) at pH 7.2, support this concept. Transient binding of Ca ions to the loop L67 and a movement of the Ca-loaded loop are discussed as a mechanism that facilitates the entrance of both Ca ions into the access channel to the ion-binding sites.

Item Type:

Journal Article (Original Article)

Division/Institute:

04 Faculty of Medicine > Pre-clinic Human Medicine > Institute of Biochemistry and Molecular Medicine

UniBE Contributor:

Peinelt, Christine

Subjects:

500 Science > 570 Life sciences; biology
600 Technology > 610 Medicine & health

ISSN:

0006-3495

Publisher:

Biophysical Society

Language:

English

Submitter:

Christine Peinelt

Date Deposited:

14 Jun 2018 16:01

Last Modified:

14 Jun 2018 16:01

Publisher DOI:

10.1529/biophysj.105.068411

PubMed ID:

16040761

BORIS DOI:

10.7892/boris.97468

URI:

https://boris.unibe.ch/id/eprint/97468

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