Abstract
Short-pulse saturation recovery electron spin resonance methods have been used to measure lateral diffusion of nitroxide-labeled lipids in multilamellar liposomal dispersions. Nitroxides with 14N and 15N isotopes introduced both separately and together were used. Differential equations have been written and solved for complex saturation recovery signals involving several superimposed exponentials. The time constants contain various combinations of the spin-lattice relaxation time (T1e) for both isotopes, Heisenberg exchange rates, and nuclear spin-lattice relaxation times (T1n). Signals of high quality were fitted by Monte Carlo variation of the amplitudes and time constants. The reliability of the approach was tested extensively by verifying that (i) the predicted number of exponentials agreed with the experimental number, (ii) relaxation parameters that were determined were independent of the observed hyperfine transition, (iii) the time constants were independent of saturating pulse length, (iv) T1e and T1n do not change when Heisenberg exchange is changed by varying the concentration, and (v) Heisenberg exchange is indeed proportional to the concentration. It has been established that bimolecular collision rates over a wide range of conditions can be reliably measured using the methodology described here. The methods depend on the favorable match of bimolecular collision rates at micromolar concentrations to nitroxide spin-lattice relaxation probabilities.
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Selected References
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- Fajer P., Thomas D. D., Feix J. B., Hyde J. S. Measurement of rotational molecular motion by time-resolved saturation transfer electron paramagnetic resonance. Biophys J. 1986 Dec;50(6):1195–1202. doi: 10.1016/S0006-3495(86)83562-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Feix J. B., Popp C. A., Venkataramu S. D., Beth A. H., Park J. H., Hyde J. S. An electron-electron double-resonance study of interactions between [14N]- and [15N]stearic acid spin-label pairs: lateral diffusion and vertical fluctuations in dimyristoylphosphatidylcholine. Biochemistry. 1984 May 8;23(10):2293–2299. doi: 10.1021/bi00305a032. [DOI] [PubMed] [Google Scholar]
- Kusumi A., Subczynski W. K., Hyde J. S. Oxygen transport parameter in membranes as deduced by saturation recovery measurements of spin-lattice relaxation times of spin labels. Proc Natl Acad Sci U S A. 1982 Mar;79(6):1854–1858. doi: 10.1073/pnas.79.6.1854. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Lai C. S., Wirt M. D., Yin J. J., Froncisz W., Feix J. B., Kunicki T. J., Hyde J. S. Lateral diffusion of lipid probes in the surface membrane of human platelets. An electron-electron double resonance (ELDOR) study. Biophys J. 1986 Sep;50(3):503–506. doi: 10.1016/S0006-3495(86)83487-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Popp C. A., Hyde J. S. Electron-electron double resonance and saturation-recovery studies of nitroxide electron and nuclear spin-lattice relaxation times and Heisenberg exchange rates: lateral diffusion in dimyristoyl phosphatidylcholine. Proc Natl Acad Sci U S A. 1982 Apr;79(8):2559–2563. doi: 10.1073/pnas.79.8.2559. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Träuble H., Sackmann E. Studies of the crystalline-liquid crystalline phase transition of lipid model membranes. 3. Structure of a steroid-lecithin system below and above the lipid-phase transition. J Am Chem Soc. 1972 Jun 28;94(13):4499–4510. doi: 10.1021/ja00768a015. [DOI] [PubMed] [Google Scholar]