Thermodynamics of Lipid Membrane Solubilization by Sodium Dodecyl Sulfate  Sandro Keller, Heiko Heerklotz, Nadin Jahnke, Alfred Blume  Biophysical Journal  Volume 90, Issue 12, Pages 4509-4521 (June 2006) DOI: 10.1529/biophysj.105.077867 Copyright © 2006 The Biophysical Society Terms and Conditions

Figure 1 Solubilization as monitored by right-angle light scattering at 25°C (A, open symbols) and 65°C (B, solid symbols). Scattering intensity at a wavelength of 632.8nm, I, versus SDS concentration, cD. Initial POPC LUV concentrations in the cuvette were 0.1mM (squares), 0.2mM (circles), 0.3mM (up-triangles), 0.5mM (down-triangles), 1.0mM (diamonds), 1.5mM (left triangles), 2.0mM (right triangles), and 2.5mM (pentagons, breakpoints indicated by arrows). I was registered 3min after addition of SDS, which was sufficient to attain equilibrium at 65°C but not at 25°C. Biophysical Journal 2006 90, 4509-4521DOI: (10.1529/biophysj.105.077867) Copyright © 2006 The Biophysical Society Terms and Conditions

Figure 2 Reconstitution as monitored by right-angle light scattering at 25°C (open symbols, near the ordinate) and 65°C (solid symbols). Scattering intensity at a wavelength of 632.8nm, I, versus POPC concentration, cL. Initial SDS concentrations in the cuvette were 0 (squares), 1.0mM (circles), 1.5mM (up-triangles), 2.0mM (down-triangles), 2.5mM (diamonds), 5.0mM (left triangles), 7.5mM (right triangles), and 10mM (pentagons, breakpoint indicated by arrow). I was registered 3min after addition of POPC, which was sufficient to attain equilibrium at 65°C but not at 25°C. Biophysical Journal 2006 90, 4509-4521DOI: (10.1529/biophysj.105.077867) Copyright © 2006 The Biophysical Society Terms and Conditions

Figure 3 ITC solubilization experiment at 65°C. Three-microliter aliquots of 50mM SDS were titrated to 1.0mM POPC LUVs. Only 60 out of 100 injections are shown. (A) Differential heating power, Δp, versus time, t. (B) Normalized heats of reaction, QD, versus SDS concentration in the cell, cD. Experimental data (circles) and simulation (solid line) according to Eqs. 17–22. b, b+m, and m denote the ranges where, in addition to the aqueous phase, only bilayers, bilayers and micelles in coexistence, and only micelles are present, respectively. Biophysical Journal 2006 90, 4509-4521DOI: (10.1529/biophysj.105.077867) Copyright © 2006 The Biophysical Society Terms and Conditions

Figure 4 ITC reconstitution experiment at 65°C. Three-microliter aliquots of 20mM POPC LUVs were titrated to 3.0mM SDS. Only 60 out of 100 injections are shown. (A) Differential heating power, Δp, versus time, t. (B) Normalized heats of reaction, QL, versus POPC concentration in the cell, cL. Experimental data (circles) and simulation (solid line) according to Eqs. 17–22. The values m, b+m, and b denote the ranges where, in addition to the aqueous phase, only micelles, bilayers and micelles in coexistence, and only bilayers are present, respectively. Biophysical Journal 2006 90, 4509-4521DOI: (10.1529/biophysj.105.077867) Copyright © 2006 The Biophysical Society Terms and Conditions

Figure 5 Phase diagram of dilute aqueous SDS/POPC mixtures. Data were taken from solubilization (circles) and reconstitution (triangles) experiments conducted with light scattering (open symbols) and titration calorimetry (solid symbols). Linear regression analyses for the onset (solid line) and the completion (dashed line) of solubilization correspond to Eqs. 2 and 4, respectively, and separate the bilayer (b) and the micellar (m) areas from the transition range (b+m). Note that the aqueous phase is always present. cL and cD are the concentrations of POPC and SDS, respectively. Biophysical Journal 2006 90, 4509-4521DOI: (10.1529/biophysj.105.077867) Copyright © 2006 The Biophysical Society Terms and Conditions

Figure 6 ITC partitioning experiment at 65°C. 10-μL aliquots of a mixture consisting of 1.5mM SDS and 1.0mM POPC LUVs were injected to SDS at different concentrations. (A) Differential heating power, Δp, of the respective third peak of five independent titrations into the calorimeter cell containing SDS at the concentrations indicated in the panel. (B) Normalized heats of reaction, QL+D, versus SDS concentration in the cell, cD. Experimental data (circles) and linear regression analysis (solid line). Biophysical Journal 2006 90, 4509-4521DOI: (10.1529/biophysj.105.077867) Copyright © 2006 The Biophysical Society Terms and Conditions

Figure 7 Partition coefficient of SDS between the bulk aqueous phase and POPC bilayers, KDb/aq, as a function of the total detergent concentration in the syringe, cDs. The concentration of POPC LUVs was cLs=1.0   mM. Experimental data as given by Eq. 8 (circles) and theoretical predictions according to Eq. 11 and KDb/i=1.4×106, calculated either without considering counterion binding by using Eqs. 12 and 13 (dashed line) or upon including Na+ adsorption to DS− by using Eqs. 12 and 16 (solid line). Biophysical Journal 2006 90, 4509-4521DOI: (10.1529/biophysj.105.077867) Copyright © 2006 The Biophysical Society Terms and Conditions