[Membrane regulation of brain Na,K-ATPase inhibition by calcium ions]

In contrast to the purified enzyme. Na, K-ATPase from intact synaptic membranes is inhibited by Ca2+ according to a biphase pattern at Ca2+ concentrations of 10(-6) to 10(-3) M. The membrane damage after three washings with bidistilled water results in elimination of low cocentration phase. Recombination of the sediment and the supernatant restores the initial shape of the inhibition curve. Dithiothreitol greatly increases the inhibition by low Ca concentrations. This effect is absent in the purified enzyme preparation and is considerably reduced after the membrane damage. Recombination restores the dithiothreitol effect. It is suggested that the sensitivity of membrane Na,K-ATPase to low concentrations of Ca2+ is controlled by the components (most likely, peripheral proteins), which are loosely bound to the membrane, this process being dependent on the degree of the SH-group reduction.