Release of Small Polyuronides from Nitella Cell Walls during Ionic Exchange

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Abstract
Mono-divalent ion exchange in isolated cell walls of Nitella flexilis (L.) Ag. induces a marked loss of wall polymers and a decrease in the wall cationic exchange capacity. These data correlate with the replacement in the walls of adsorbed Mn(2+) by Na(+) ions. Boiling wall samples in methanol for 1 h or keeping the ionic solutions chilled to 4 degrees C does not inhibit the cell wall polymer leakage but modifies the kinetics both of the ionic exchange and of the released polymers. These data are more compatible with physical rather than enzymic induced processes. The extracted polymers in the successively renewed NaCl solutions initially belong to the wall protein and pectin fractions and mainly to pectic fractions subsequently. Determination of the average degree of polymerization shows that the average molecular size of the lost acidic polysaccharides increases with extraction time up an average polymerization degree of 25. Enzyme-linked immunosorbent assay inhibition tests show the presence of homopolymer blocks equal to or higher than 10 in the released polymer fragments. Compositional analysis of released polysaccharides suggests that the pectin lost by action of monovalent ions was largely composed of rhamnogalacturonans whose acidic residue fraction is approximately 60% in association with galactose chains. Small quantities of glucuronylated xylans are also found.