PubMed · 4553528
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I Fukui, H Kushiro. 1972. [Total lipids].. https://pubmed.ncbi.nlm.nih.gov/4553528/
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A method to detect leakage of water-soluble intercalators such as ethidium bromide and propidium iodide from liposomes (egg-lecithin and egg-lecithin/cholesterol) by means of fluorescence is presented. The addition of excess DNA outside the liposomes brings about intercalation of released dye with the DNA. The increase in fluorescence intensity that results from the dye-DNA complex is used to detect the degree of dye release. Titration and surfactant-induced leakage measurements display the suitability of the method. Spontaneous leakage measurements show that propidium has much lower leaking rates than those of ethidium. This is probably due to the less lipophilicity of propidium as estimated from the partition coefficients between octanol and medium. Stabilizing the egg-lecithin membranes with cholesterol strongly reduces the leaking rates for ethidium while no effect is detected for the slow leaking rates of propidium. Lowering the temperature from 25 to 6 degrees C results in lower leaking rates for both dyes.
We previously described the synthesis of two deuterium-labelled sphingoid bases, which made it possible to perform NMR spectroscopy on this family of signalling modulators in membranes (Rigby, A.C, Barber, K.R and Grant, C.W.M. (1995) Biochim. Biophys. Acta 1240, 75-82). In the present work we sought to test the concept that such mediators may display altered physical behaviour through association with anionic lipids - as a possible mechanism of involvement in signal transduction. Lyso-dihydrogalactosylceramide with deuterium nuclei at C4 and C5 of the sphingosine backbone and at C'3 and C'4 of the galactose ring ([2H4]lyso-GalCer), and N,N-dimethylsphingosine with deuterated amino-methyl groups ([2H6]dimethylsphingosine), were assembled as minor components into unsonicated fluid bilayer membranes of 1-palmitoyl-2-oleoylphosphatidylcholine/cholesterol. The effect of (anionic) phosphatidylserine was considered in this zwitterionic host matrix. The results present a picture of rapidly reversible interaction. The (-) charged phosphatidylserine exerted readily-measurable control over the orientation of the carbohydrate residue of [2H4]lyso-GalCer. In contrast, surrounding (-) charges exerted little spectral influence at the level of C4 and C5 of the lyso-GalCer, membrane-inserted, backbone; or at the level of the amino group of dimethylsphingosine. It would appear that packing alterations induced by the phosphatidylserine/sphingoid base association can translate into sizeable spatial constraints in the neighbouring aqueous domain.
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