FIGURE 9.

Quenching of KcsA fluorescence in mixtures with cardiolipin. KcsA was reconstituted into bilayers containing mixtures of BrPC and TOCL (□) and BrCL and DOPC (○). Fluorescence intensities are expressed as F/F_o where F_o is the fluorescence intensity in the nonbrominated lipid. The solid line for the BrPC/TOCL experiment shows a fit to Eq. 2 giving the annular binding constant and the lines for the BrCL/DOPC experiments show fits to the annular/non-annular binding site model, assuming (solid line) that all the fluorescence can be quenched from the non-annular sites (Eq. 5) and (broken line) that only 60% of the fluorescence can be quenched from the non-annular sites (Eq. 6). Values for the binding constants are listed in Table 3. The buffer was 20 mM HEPES and 1 mM EGTA at pH 7.2. The mole fraction of cardiolipin was calculated on a chain basis to account for the fact that cardiolipin contains four fatty acyl chains and phosphatidylcholine, two.