Glycoproteins from the cell wall of Phaseolus coccineus

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Abstract
The use of a modified sodium chlorite/acetic acid delignification procedure for the solubilization of a hydroxyproline-rich glycoprotein fraction from the depectinated cell walls of P. coccineus is described. The crude glycoprotein was associated with some pectic material; hydroxyproline and serine were the most abundant amino acids, and arabinose, galactose and galacturonic acid the predominant monosaccharides. The bulk of the hydroxyproline is O-glycosidically substituted with tetra- and tri-arabinofuranosides. The linkages in these arabinosides could be inferred from methylation analysis. Ion-exchange chromatography of the crude glycoprotein gave 1 major and 2 minor hydroxyproline-rich fractions, with similar amino acid but different monosaccharide composition. In the major fraction, serine appears to be O-glycosidically substituted with a single galactopyranoside residue that can be removed by the action of .alpha.-galactosidase but not .beta.-galactosidase. Removal of arabinofuranoside residues by partial acid hydrolysis greatly enhanced the action of .alpha.-galactosidase. Methylation followed by carboxy reduction with LiAl2H4 has shown the presence of (1 .fwdarw. 4)-linked galacturonic acid in the crude glycoprotein fraction but not in the major fraction from the ion-exchange column. The bulk of the pectic material is not associated with the major glycoprotein component. The glycoprotein may be held in the wall by phenolic cross-links. Similarities with the glycopeptide moiety of potato lectin provides further evidence for a class of hydroxyproline-rich glycoproteins with common features.