TRANSGLUTAMINASE-CATALYZED GLYCOSYLATION OF VEGETABLE PROTEINS - EFFECT ON SOLUBILITY OF PEA LEGUMIN AND WHEAT GLIADINS

Transglutaminase was used to covalently attach glycosyl units to glutamine residues of legumin and beta-gliadins. To prevent epsilon-(gamma-glutamyl)lysine cross-link formation, the lysine residues of legumin and beta-gliadins were first blocked by reductive alkylation. In this way, the percentage of modification of amino groups was 84% for legumin and 100% for beta-gliadins. Then, transglutaminase action resulted in incorporation of 18 and 57 glycosyl units per mole of alkylated beta-gliadins and legumin, respectively. The corresponding degree of glycosylation of glutamine residues was 15.7% with gliadins and 25.7% with legumin. The solubility of neoglycoproteins was markedly increased over that of native proteins in the range of their isoelectric points (pH(i)). This effect was much less pronounced for pH(s) far from the pH(i). For pH values below 5.0, the solubility of glycosylated beta-gliadins was even slightly lower than that of native beta-gliadins.