Mitogens-DPPC-vesicles interaction: A spin label ESR study |
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Authors: | S Belsito P Sapia L Sportelli |
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Institution: | (1) Dipartimento di Fisica, Laboratorio di Biofisica Molecolare, Università della Calabria, 87036 Arcavacata di Rende (CS), Italia |
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Abstract: | Summary The electron spin resonance spectroscopy with the spin labelling technique has been used to investigate the interaction of
sonicated di-palmitoyl-phosphatidylcholine (DPPC) small unilamellar vesicles with concanavalin A (Con A), phytohemagglutinin
(PHA) and staphylococcal enterotoxin B (SEB) in the temperature range 0–50°C. Conventional ESR measurements show that the
addition of mitogens to the vesicles suspensions up to the number of mitogens/number of vesicles ratio of 60 increases the
orientational degree of order of the lipid molecules in the gel phase and the gel→liquid-crystalline phase transition temperature.
No effects on the liquid-crystalline phase have been observed, also no matter for the mitogen used. The effectiveness results
in the order: ConA>SEB>PHA. Saturation transfer-ESR measurements evidence more restricted rotation of the DPPC molecules in
the gel phase in the presence of Con A and SEB than in the presence of PHA if compared to pure DPPC-vesicles. The effective
rotational correlation time, σc, of the spin label 5-SASL results about one order of magnitude higher in the presence of 60 mitogen molecules/vesicle. The
ESR findings suggest a mitogen-induced increase in the packing density of lipid bilayers which is attributed to a morphological
change from sonicated vesicles, with a small radius of curvature, to a more planar mesophase. Con A is more effective than
SEB and PHA in inducing this process.
The authors of this paper have agreed to not receive the proofs for correction. |
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Keywords: | Molecular biophysics |
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