Ca2+ stabilization of respiratory Complex I from Escherichia coli

Abstract

Stability of the membrane-bound and purified H⁺-translocating NADH:ubiquinone oxidoreductase, Complex I, was studied. The loss of the enzyme activity is strongly increased by alkaline pH and dilution of the sample. Complex I inactivation is prevented specifically by a low concentration of Ca²⁺ and/or an intracellular stabilization factor (ISF). The action of both, Ca²⁺ and ISF, on Complex I stability is interdependent. The data are discussed in terms of a release of structural Ca²⁺ as a reason for Complex I decay and an effect of ISF on the affinity and/or accessibility of Ca²⁺ binding site.