We are performing experiments which compare the anisotropies of a lipid liposome (DOPC and DPPC) with and without a drug, against temperature (graph of anisotropy vs temperature from 28-52C). At the moments we performed fluorescence anisotropies with TMA-DPH label. We would like to perform the same with DPH. If we observe a greater slope/gradient with the dph, what does that mean? Is it that the drug is embedded closer to the hydrophobic region? Is the effect of a molecule/drug over the membrane more internal with the DPH probe or more external with TMA-DPH ?
Dear Ayush Kris ,
The short answer is probably yes.
DPH is hydrophobic and is often used to monitor the hydrophobic core of the bilayer. TMA-DPH is believed to monitor the more shallow regions of the bilayer (glycerol backbone and upper segments of the phospholipid acyl chains), the cationic group present in TMA-DPH is supposed to act as an anchor to the water/bilayer interface.
See for a recent comparison between the two and relevant references:
do Canto, A. M., Robalo, J. R., Santos, P. D., Carvalho, A. J. P., Ramalho, J. P., & Loura, L. M. (2016). Diphenylhexatriene membrane probes DPH and TMA-DPH: A comparative molecular dynamics simulation study. Biochimica et Biophysica Acta (BBA)-Biomembranes, 1858(11), 2647-2661.
https://www.sciencedirect.com/science/article/pii/S0005273616302668
So if the drug is able to alter the observed anisotropy of DPH then this indicates that the drug is able to insert deeper into the bilayer.
Hope this answers your question to some degree.
Best regards.
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