Nature des liaisons de l'ion calcium dans la paroi de Nitella flexilis

Spectrophotometric titrations and conductivity measurements show that Nitella cell walls contain nonexchangeable Ca2+ cations which are probably chelated by COO− anions and donor groups such as OH (from polysaccharides) or NH (from proteins).A large part of these calcium ions are removed by acidification of the external medium. Subsequent augmentation of COO− groups increases the number of exchange sites available for H+ and K+ ions. The variation of the carboxylic groups concentration (α) is thus not fully accounted for by the pK of polygalacturonic acids but is also related to changes within the constitutive calcium of the cell wall.