ALFALFA-STEM PECTINS - ENZYMATIC DEGRADATION AND STRUCTURAL CHARACTERIZATION OF A BUFFER-SOLUBLE FRACTION

Carbohydrate material solubilized from alfalfa (Medicago sativa L.) stem cell walls with hot 10mM potassium phosphate (pH 7.0) was fractionated into neutral and acidic components by anion-exchange chromatography. Glycosyl-composition and glycosyl-linkage analysis indicated that the neutral fraction contained arabinogalactan type I and that the major acidic fraction was composed of rhamnogalacturonans. The rhamnogalacturonans were resistant to depolymerization by endo-(1 --> 4)-alpha-D-galacturonanase. Saponification of the rhamnogalacturonans followed by acidification to pH 5 gave a precipitate and a soluble fraction. The precipitate after resolubilization was extensively depolymerized by endo-(1 --> 4)-alpha-D-galacturonanase. Rhamnogalacturonans in the soluble fraction, which contained a high proportion of neutral sugar residues, were only partially depolymerized by endo-(1 --> 4)-alpha-D-galacturonanase. Products separated by gel filtration were shown by glycosyl-composition analysis to be composed of different proportions of neutral sugar residues and galactosyluronic residues.