Journal of Experimental Botany, Vol 49, 797-805, Copyright © 1998 by Oxford University Press
C Gillet, M Voue and P Cambier
The types of binding of different mono- and divalent ions to sites of the
constitutive pectic acids of the Nitella cell walls
were investigated by performing ion exchanges at different pH. The
experimental results were then analysed in the framework of a model derived
from the polyelectrolyte theory in which the competitive process of
dissociation of the exchange sites and their complexation by counterions
are taken into account. Divalent ions Ca2+ and
Mn2+ interacted specifically with the exchange sites
to give rise to strong thermodynamic association constants. They also
induced conformational transitions of the pectic acids which allowed some
site-specific association with monovalent ions, although the latter, in the
absence of divalent ions, interacted only in a purely electrostatic manner
with the charged sites. The complexation phenomenon of the monovalent ions
also results in a feedback process which enhances or depletes the
site-specific interactions of the divalent counterions. Changes in the
counterion association with the wall exchange sites will take place without
modification in the wall electrostatic field, when divalent ions are
present at the usual pH. These specific interactions are supported by the
values of the residual interaction energy, calculated from the variations
of the apparent pKa of the polygalacturonic acids with
their degree of protonation.Keywords: Plant cell wall,
counterion binding, polygalacturonate, conformational transition,
Nitella flexilis.
ARTICLES
Site-specific counterion binding and pectic chains conformational transitions in the Nitella cell wall
Unite de Biotechnologie Theorique, Facultes Universitaires Notre-Dame de la Paix, 61 Rue de Bruxelles, B-5000 Namur, Belgium; Centre de Recherche en Modelisation Moleculaire, Universite de Mons-Hainaut, 20 Place du Parc, B-7000 Mons, Belgium; Corresponding author
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