THE INFLUENCE OF MEMBRANE FLUIDITY ON CALCIUM DEPENDENT ATPase FROM SARCOPLASMIC RETICULUM FROM SKELETAL MUSCLE
Abstract
The ATPase from sarcoplasmic reticulum was reconstituted using either DMPC or DPPC in order to obtain a lipid-protein system with a single lipidic component and only one type of protein. The effects of the lipidic microenvironment on the protein have been studied through changes in enzyme activity at different temperatures and with different phospholipid composition of the membrane. The results obtained after the dependence of ATPase activity on temperature reveal an increase of activation energy at the transition temperature of the phospholipid (Te) and also at a temperature lower than Te corresponding to the fusion of lipid-protein patches. ATPase reconstituted with DPPC did not follow a Michaelis-Menten type of kinetic model in which activation by excess of substrate (ATP) is proposed. A study of the proposed kinetic parameters showed that all of them notably increased at approximately 30°C. being this temperature below Te for DPPC (41ºC). This is thetemperature at which the protein-rich lipid-protein patches melted in the DPPC-ATPase samples.Downloads
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