Abstract
The uptake of Ca++ by reconstituted proteoliposomes involves an ATP-independent as well as an ATP-dependent process. In the presence of 0.7 mM ATP, 1 mM dibucaine inhibited Ca++ uptake and (Mg++ + Ca++)-ATPase activity, but 0.2 mM dibucaine stimulated both. The latter reduced the velocity of ATP-independent Ca++ uptake at low Ca++ concentrations, but increased it at a high concentration (0.15 mM of Ca++. ATP-dependent Ca++ uptake was facilitated by 0.2 mM dibucaine only in the presence of a high concentration of Ca++. Kinetic analyses of the data obtained with the lower dose of dibucaine suggest that this compound competes with Ca++ for binding sites on the outer surface of membranes and that its interaction with Ca++ induces a conformational change of membranes accompanied by an increase in the passive permeability of Ca++ and activation of the ATP-mediated Ca++ pump.
- Copyright © 1978 by Academic Press, Inc.
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