ISSN:
1432-1017
Keywords:
DGDG membranes
;
Digalactosyldiacylglycerol
;
FTIR
;
Divalent cations
;
Intramolecular H-bonding
;
Ion-binding
;
Membrane aggregation
;
Monovalent cations
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Physics
Notes:
Abstract Lipid bilayers composed of digalactosyldiacyl-glycerol (DGDG), that is, Galpα1-6Galpβ1-3DAG, a non-ionic lipid of the thylakoid membrane of chloroplasts, aggregate in aqueous media containing mono- and divalent cations in amounts above a threshold concentration (Ct) of about 1.0, 4.7 and 10.0 mM for Ca2+, Mg2+ and Na+, respectively. In this work, we found that above Ct the DGDG membranes do not undergo fusion and that the aggregation can be reversed, or disrupted. This means that the perturbation induced by the salts results from adsorption, or complexation of the ions in the polar head of DGDG. To investigate this question, we used Fourier transform infrared (FTIR) spectroscopy to identify the molecular sites in DGDG which are modified by interaction, or adduct formation with CaCl2, MgCl2 and NaCl. We also determined whether the ions affect the intramolecular hydrogen bonding between the sn2 ester C = O and the carbon-6 of the α-anomer of galactose (Gal). The major conclusions are: (i) the salts do not affect, at least directly, the, ester carbonyl region of DGDG, (ii) the most probable sites of binding, or adsorption, for the ions are the ring oxygen, and (iii) the ring hydroxyls are the sites of either ion complexation or intra- and intermolecular H-bonding in interacting DGDG membranes. Within this framework, the complexation of the ions with Gal might induce total or partial dehydration of the galactolipid headgroup and thus provides the means to overcome the repulsive hydration forces that hinder aggregation of the DGDG membranes.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00180259
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