[Study of lipid-protein interactions in mitochondrial membranes using the intrinsic fluorescence of tryptophan]

The environment of membrane-bound proteins has been investigated by measuring the fluorescence of intrinsic tryptophans in intact bovine heart mitochondria, in lipid-depleted mitochondria, and in reconstituted mitochondria. Lipid depletion induces a strong decrease of fluorescence intensity, probably as the result of extraction of peripheral proteins by the solvents used. Comparison of lipid-depleted and lipid-reconstituted mitochondria shows a higher fluorescence in the lipid-depleted membranes; in an Arrhenius plot the fluorescence intensity shows two breaks in the lipid-depleted membranes, but no break in the reconstituted ones. Butanol has little effect on fluorescence intensity of intact mitochondria. The results are compatible with a constant lipid environment of integral proteins which is not modified by either temperature or organic solvents.