Lipid-protein interactions and rotational diffusion

and 12.1 mol/moL The figure is adapted from [24] with permission from the American Chemical Society 

24 lipid/peptide titration of the K26 peptide complexes with DMPC obtained from ESR difference spectra of various spin labels 14-PASL phosphatidic acid (o), 14-SASL Stearic acid ( ), 14-PSSL phosphatidylserine (A), 14-PGSL, phosphatidylglycerol ( ), and 14-PCSL phosphatidylcholine ( ) spin labels. The ratio of nP/nb (fluid/restricted) is calculated from the double integrated intensity of the fluid and motionally restricted components in the ESR spectra. The figure is adapted [24] by permission of the American Chemical Society 

The amount of the restricted component increases with an increase of the peptide. It is found that the peptide molecules slow down the rate of rotational motion of the lipid chains when the interaction is strong. The dependence of the ratio of the intensity of the fluid component to that of the motionally restricted component (nf /nb ) is given as a function of the lipid/peptide ratio of the complexes (nt) for the different spin-labeled lipid as shown in Fig. 8.24. 

The data are displayed in terms of the equation for equilibrium lipid-peptide association  

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L. I. Horvath, T. Heimburg, P. Kovachev, J. B. C. Findlay, K. Hideg, D.Marsh, Integration of a K+ channel-associated peptide in a lipid bilayer Conformation, lipid-protein interactions, and rotational diffusion. Biochemistry 34 (1995) 3893. 

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