Soluble and wall-bound glycoproteins of apple fruit tissue

Apple fruit tissue contains small amounts of readily soluble glycoproteins, rich in hydroxyproline; polymethylgalacturonide is not covalently bound to the soluble glycoproteins. Barium hydroxide hydrolysis of apple fruit cell walls liberated glycopeptides containing 4 arabinosyl residues per hydroxyprolyl residue, which were attacked very slowly by α-l-arabinofuranosidase. Hydrazinolysis liberated similar glycopeptides, which were difficult to separate from a polysaccharide containing galactose residues. Protease treatment of walls also released glycopeptides containing hydroxyproline, and a small proportion of these were associated with polyuronide. Polygalacturonase pretreatment of walls led to increased release of hydroxyprolyl residues by protease. Susceptibility of the hydroxyproline containing glycoprotein in the cell wall to attack by protease and arabinosidase did not change during fruit ripening. The amount of an unknown hexosamine associated with the wall was less in ripethan in unripe fruit.