Effect of Cations on the Elution of Pectic Polysaccharides from Anion-Exchange Resins

Abstract

Conditions for quantitatively eluting six plant pectic polysaccharides from diethylaminoethyl (DEAE) columns were established. Cations, surprisingly, greatly affected the elution of pectic polysaccharides from these anion-exchange columns. Quantitative elution of apple pectic acid was achieved when columns of DEAE-Sephadex A-25 and DEAE-Trisacryl Plus-M were developed with 0.5 M NH4Cl, 0.5 M LiCl, or 0.5 M CsCl in buffer. In contrast, up to 1 M NaCl and KCI in buffer only eluted 6.3 to 54% of the apple pectic acid from the two types of columns. In each ease the retained apple pectic acid was eluted basically quantitatively by 0.5 M NH4Cl in buffer. The elution of a pectic polysaccharide fraction from Apium graveolens (celery), commercial citrus polygalacturonic acid, and two polysaccharides isolated from purified cell walls of Lemna minor (duckweed) from columns of DEAE-Trisacryl was incomplete when the columns were developed with 0.5 M NaCl or 0.5 M KCI in buffer, ranging from 0 to 89%; however, again, the retained portion of each sample was eluted quantitatively or almost so from the columns with 0.5 M NH4Cl in buffer. One pectic polysaccharide, commercial citrus pectin, was eluted equally well and almost quantitatively by 0.5 M NaCl, KCI, and NH4Cl in buffer. When a pectic polysaccharide fraction from purified cell walls of L. minor was applied to a preparative column of DEAE-Trisacryl Plus-M, 99% of the sample was eluted by a gradient of 0 to 0.5 M NH4Cl in buffer. In a basically identical experiment, only 55% of the sample was eluted with a gradient of 0 to 0.5 M NaCl in buffer. The discovery that NH1+4 ion in the eluent brings about the essentially quantitative elution of pectic polysaccharides from anion-exchange resins solves the long-standing problem of incomplete recovery of pectic polysaccharides from DEAE-columns. Li1+ and Cs1+ ions are similar to NH1+4 ion in elution effectiveness.