Figure 4.

Functional dependence of relaxation rates on CH bond order parameters in simulated bilayers. Data are shown for: (A) DMPC bilayer in the absence of cholesterol (blue) and (B) DMPC containing 50 mol % cholesterol (Chol) (red). Profiles of spin-lattice relaxation rates (R_1Z, top) and order parameters (S_CD, bottom) are plotted as a function of carbon position along the sn-1 and sn-2 chains of DMPC. (C) Same data but now replotted as the R_1Z relaxation rate as a function of the squared S_CD order parameter. Best linear fits to carbons (on both chains) C4 through C13 for 0 mol % cholesterol and C10 through C13 for 50 mol % cholesterol are shown in blue and red, respectively. Carbon atoms outside of these ranges deviate from the linear relationship. Note that the relaxation rates and order parameters exhibit a square-law dependence both with and without cholesterol. All simulations were performed at 44°C. See text for further details. To see this figure in color, go online.