FIGURE 1 .

Transmembrane profile of oxygen-induced T₁-relaxation enhancement of spin-labeled lipids, n-PCSL (▪), and spin-labeled peptide, WALP (○), in fluid phospholipid bilayer membranes; data from Dzikovski et al. (9) and Nielsen et al. (1), respectively. (A) Lipid relaxation enhancements deduced from convolution linewidths: ΔΔH_L = Δ(1/T_1e)/γ_e, compared with peptide relaxation enhancements deduced from saturation recovery EPR. (B) Lipid relaxation enhancements deduced from CW-EPR saturation parameters: , compared with peptide relaxation enhancements deduced from saturation recovery EPR. Solid and dashed lines are nonlinear least-squares fits of Eq. 2 to the data for spin-labeled lipids and peptides, respectively. Relaxation enhancements are normalized such that R₁ − R₂ = 1 and R₂ = 0, for the fits of Eq. 2; transmembrane distances are referred to the membrane midplane as origin.