Spin-Lattice Relaxation Rates of Lipid Spin Labels as a Measure of Their Rotational Diffusion Rates in Lipid Bilayer Membranes. Membranes (Basel) 2022 Sep 30;12(10)
Date
10/28/2022Pubmed ID
36295720Pubmed Central ID
PMC9612125DOI
10.3390/membranes12100962Scopus ID
2-s2.0-85140781071 (requires institutional sign-in at Scopus site) 1 CitationAbstract
The spin-lattice relaxation rate (T1-1) of lipid spin labels obtained from saturation recovery EPR measurements in deoxygenated membranes depends primarily on the rate of the rotational diffusion of the nitroxide moiety within the lipid bilayer. It has been shown that T1-1 also can be used as a qualitative convenient measure of membrane fluidity that reflects local membrane dynamics; however, the relation between T1-1 and rotational diffusion coefficients was not provided. In this study, using data previously presented for continuous wave and saturation recovery EPR measurements of phospholipid analog spin labels, one-palmitoyl-2-(n-doxylstearoyl)phosphatidylcholine in 1,2-dimyristoyl-sn-glycero-3-phosphorylcholine/cholesterol membranes, we show that measured T1-1 values are linear functions of rotational diffusion of spin labels. Thus, these linear relationships can be used to transfer T1-1 values into spin label rotational rates as a precise description of membrane fluidity. This linearity is independent through the wide range of conditions including lipid environment, depth in membrane, local hydrophobicity, and the anisotropy of rotational motion. Transferring the spin-lattice relaxation rates into the rotational diffusion coefficients makes the results obtained from saturation recovery EPR spin labeling easy to understand and readily comparable with other membrane fluidity data.
