1 research outputs found
A theory of Plasma Membrane Calcium Pump stimulation and activity
The ATP-driven Plasma Membrane Calcium pump or Ca(2+)-ATPase (PMCA) is
characterized by a high affinity to calcium and a low transport rate compared
to other transmembrane calcium transport proteins. It plays a crucial role for
calcium extrusion from cells. Calmodulin is an intracellular calcium buffering
protein which is capable in its Ca(2+) liganded form of stimulating the PMCA by
increasing both the affinity to calcium and the maximum calcium transport rate.
We introduce a new model of this stimulation process and derive analytical
expressions for experimental observables in order to determine the model
parameters on the basis of specific experiments. We furthermore develop a model
for the pumping activity. The pumping description resolves the seeming
contradiction of the Ca(2+):ATP stoichiometry of 1:1 during a translocation
step and the observation that the pump binds two calcium ions at the
intracellular site. The combination of the calcium pumping and the stimulation
model correctly describes PMCA function. We find that the processes of
calmodulin-calcium complex attachment to the pump and of stimulation have to be
separated. Other PMCA properties are discussed in the framework of the model.
The presented model can serve as a tool for calcium dynamics simulations and
provides the possibility to characterize different pump isoforms by different
type-specific parameter sets.Comment: 24 pages, 6 figure