Protein-lipid interaction: Biophysical studies of (Ca 2+ + Mg 2+)-ATPase reconstituted systems

Abstract

Differential scanning calorimetry, fluorescence spectroscopy and freeze-fracture electron microscopy have been applied to a study of the reconstituted Ca 2+-ATPase proteins from sarcoplasmic reticulum when they are incorporated into pure lipid/water systems. The results obtained with these techniques have been used to examine the effects of this intrinsic protein upon the surrounding lipid at temperatures above and below the main lipid solid-fluid phase transition temperature ( T c). 1. 1. Above this T c value, the freeze-fracture data show that the proteins are randomly distributed within the plane of the bilayer. The fluorescence data show that as the protein content in the bilayer increases, so does the ‘microviscosity’. 2. 2. Below T c the proteins occur in high protein to lipid patches, separate from the remaining crystalline lipid. The fluorescence data indicate that at these temperatures the presence of the protein causes a decrease in microviscosity, whilst the calorimetric data indicate a decrease in enthalpy of the main lipid transition.