TY - JOUR
T1 - Solubilization of DMPC and DPPC vesicles by detergents below their critical micellization concentration
T2 - high-sensitivity differential scanning calorimetry, Fourier transform infrared spectroscopy and freeze-fracture electron microscopy reveal two interaction sites of detergents in vesicles
AU - Bayer, Thomas M.
AU - Werner, Gerd Dieter
AU - Sackmann, Erich
PY - 1989/9/4
Y1 - 1989/9/4
N2 - The interaction of sodium deoxycholate, sodium cholate and octyl glucoside with sonicated vesicles of lα-dimyristoyl-phosphatidylcholine (DMPC) and lα-dipalmitoylphosphatidylcholine (DPPC) at concentrations below the critical micellization concentration (cmc) of the detergents was studied by high-sensitivity DSC (hs-DSC), Fourier transform infrared spectroscopy (FT-IR) and freeze-fracture electron microscopy. The two phospholipids exhibited a striking different thermotropic behaviour in the presence of these detergents. For DPPC vesicles, the detergents were found to interact exclusively in the aqueous interface region of the bilayer below the membrane saturation concentration Rsat while in DMPC vesicles two coexisting interaction sites below this concentration persist. These are detergents which interact at the aqueous interface region (site 1) and in the acyl chain region (site 2) of the DMPC vesicles. The partition coefficients K of the detergents between DPPC vesicles and the water phase were calculated from the hs-DSC results at two detergent/phospholipid molar ratios Rtot ≤ Rsat as 0.35, 0.049 and 0.040 mol-1 for sodium deoxycholate, sodium cholate and octyl glucoside, respectively. In contrast, for DMPC the K values for Rtot ≤ Rsat were found to be dependent on Rtot due to the occupation of site 2 by the detergents above a certain Rtot. The model is discussed on the basis of the detergents free energies of transfer from the water phase to site 1 and site 2 of the vesicles, respectively. The solubilization behaviour of DPPC vesicles, dependent on whether the total detergent concentration is above or below the cmc at Rsat, differed significantly as revealed by hs-DSC. This suggests that in the latter case an additional hydrophobic effect could facilitate the formation of disc shaped mixed micelles. Moreover, this different behaviour was employed to measure the cmc values of the detergents studied in the presence of the vesicles by hs-DSC.
AB - The interaction of sodium deoxycholate, sodium cholate and octyl glucoside with sonicated vesicles of lα-dimyristoyl-phosphatidylcholine (DMPC) and lα-dipalmitoylphosphatidylcholine (DPPC) at concentrations below the critical micellization concentration (cmc) of the detergents was studied by high-sensitivity DSC (hs-DSC), Fourier transform infrared spectroscopy (FT-IR) and freeze-fracture electron microscopy. The two phospholipids exhibited a striking different thermotropic behaviour in the presence of these detergents. For DPPC vesicles, the detergents were found to interact exclusively in the aqueous interface region of the bilayer below the membrane saturation concentration Rsat while in DMPC vesicles two coexisting interaction sites below this concentration persist. These are detergents which interact at the aqueous interface region (site 1) and in the acyl chain region (site 2) of the DMPC vesicles. The partition coefficients K of the detergents between DPPC vesicles and the water phase were calculated from the hs-DSC results at two detergent/phospholipid molar ratios Rtot ≤ Rsat as 0.35, 0.049 and 0.040 mol-1 for sodium deoxycholate, sodium cholate and octyl glucoside, respectively. In contrast, for DMPC the K values for Rtot ≤ Rsat were found to be dependent on Rtot due to the occupation of site 2 by the detergents above a certain Rtot. The model is discussed on the basis of the detergents free energies of transfer from the water phase to site 1 and site 2 of the vesicles, respectively. The solubilization behaviour of DPPC vesicles, dependent on whether the total detergent concentration is above or below the cmc at Rsat, differed significantly as revealed by hs-DSC. This suggests that in the latter case an additional hydrophobic effect could facilitate the formation of disc shaped mixed micelles. Moreover, this different behaviour was employed to measure the cmc values of the detergents studied in the presence of the vesicles by hs-DSC.
KW - Critical micellar concentration
KW - Detergent
KW - DSC
KW - Freeze-fracture
KW - FTIR
KW - Phospholipid vesicle
UR - http://www.scopus.com/inward/record.url?scp=0024418858&partnerID=8YFLogxK
U2 - 10.1016/0005-2736(89)90219-8
DO - 10.1016/0005-2736(89)90219-8
M3 - Article
C2 - 2765550
AN - SCOPUS:0024418858
SN - 0005-2736
VL - 984
SP - 214
EP - 224
JO - Biochimica et Biophysica Acta - Biomembranes
JF - Biochimica et Biophysica Acta - Biomembranes
IS - 2
ER -