tag:blogger.com,1999:blog-1283194685237019772.post3270165171804659949..comments2024-03-26T17:11:28.045+02:00Comments on The NMRlipids Project: Some points concerning the ion-membrane interaction resultsmarkus.http://www.blogger.com/profile/05973383391755193687noreply@blogger.comBlogger2125tag:blogger.com,1999:blog-1283194685237019772.post-57732623050222403202014-01-23T14:40:35.857+02:002014-01-23T14:40:35.857+02:00While reading the literature more carefully I real...While reading the literature more carefully I realised that the order parameters for g1 and g2 as a function of ion concentration are not actually measured in Akutsu et al. Biochemisry 20, 7366 (1981), Ref. 36 in the manuscript. However, they show that ions do not affect to the g3 order parameter and to the order parameters of the first carbons in the acyl chains. Then they conclude that:<br />"The addition of metal ions has practically no effect on the quadrupole splittings of the glycerol backbone or the fatty acyl chain segments, suggesting that the interaction with the lipid bilayer is limited to the polar region."<br /><br />In principle it is, however, possible that ions affect the g2 and/or g1 order parameter since that effect is not explicitly measured. I find it unlikely, though. I am not aware of any other experimental data where that would be measured either. I think that nowdays this could be done with ¹³C NMR without specifically dueterated samples.<br /><br />In conclusion, I think that the experimental data for g1 and g2 should be removed from Fig. 4 before actual data is found from literature, or measured by somebody.Samuli Ollilahttps://www.blogger.com/profile/06106569992787533569noreply@blogger.comtag:blogger.com,1999:blog-1283194685237019772.post-1782521174374565652014-01-07T18:04:38.050+02:002014-01-07T18:04:38.050+02:00I found a relevant publication related to the ion-...I found a relevant publication related to the ion-membrane interactions which I have not cited in the manuscript: Filippov et al. Chem. Phys. Lipids 159, 81 (2009) http://dx.doi.org/10.1016/j.chemphyslip.2009.03.007<br /><br />They measure the lipid lateral diffusion coefficients with different ion concentrations by using NMR. The lateral diffusion of DOPC is not affected up to 0.27 M concentration of NaCl, and 0.1 M concentration of CaCl_2. I find this important since one of the evidence presented for the Na+ binding into a PC headgroup has been the decreased lateral diffusion coefficient of membrane probes (Böckmann et al. Biophys. J. 85, 1647 (2003) http://dx.doi.org/10.1016/S0006-3495(03)74594-9)<br /><br />Since Filippov et al. do not find the decrease with NMR measurements they write:<br />"Thus, it seems that we are forced to conclude<br />that the lateral diffusion coefficients obtained by the fluorescence<br />methods used by Böckmann et al. (2003) are strongly dependent<br />on the fluorescent probe molecule and should be taken with<br />caution."Samuli Ollilahttps://www.blogger.com/profile/06106569992787533569noreply@blogger.com