The selective hydrolysis of tamarind seed xyloglucan (tamarind gum) using enzymes isolated from germinated nasturtium (Tropaeolum majus L.) cotyledons

Abstract

"The selective hydrolysis of tamarind seed xyloglucan (Tamarind gum) using enzymes isolated from germinated nasturtium (Tropaeobun majus L.) seeds". Background. Tamarind seed xyloglucan is a storage cell wall polysaccharide which consists of a rigid cellulose-like backbone of (l-»4)-B-D-linked glucopyranosyl units carrying both D-xylopyranosyl residues and D-galactopyranosyl-B-(l-»2)-xylopyranosyl residues. The xylosyl residue is linked a-(l-»6) on to the main glucan chain. The xyloglucan polysaccharide of the primary cell wall of growing plants has very similar composition and structure with the only exception that some terminal galactosyl residues carry L-fucosyl substituents attached a-(l-»2) (Fry, 1989; Hayashi, 1989). Mobilization of storage xyloglucan following germination in Tropaeolum is brought about by the synergistic action of at least four enzymes, namelyendo-(l-»4)-B-D-glucanase,fi-galactosidase,a-xylosidaseandB-glucosidase (Edwards et al., 1985). The aims of the project were the purification and characterization of xyloglucan-specific hydrolases from germinated nasturtium cotyledons. Results and discussion. (A) The enzyme a-xylosidase was purified to homogeneity from germinated nasturtium cotyledons and the molecular properties were investigated. The enzyme is a glycoprotein (approx. Mr 85000, on SDS-PAGE) able to remove a single unsubstituted xylosyl residue attached to the backbone glucose at the nonreducing end of the xyloglucan oligosaccharide molecule (Fanutti et al., 1991). (B) The nasturtium endoglucanase (Edwards et al., 1986) was shown to be a novel type of transferase (xyloglucan emfo-transferase) able to catalyze the transglycosylation of xyloglucan molecules (Fanutti et al., 1993). Enzymes with the same specificity of the nasturtium endoglucanase have been correlated with primary cell wall elongation (Albersheim, 1976). (C) The nasturtium B-galactosidase (Edwards et al., 1988) catalyzes the selective removal of galactose residues from polymeric xyloglucan as well as xyloglucan oligosaccharides (Edwards et al., 1988). The rheological properties of modified xyloglucan were studied. Galactose-removal led to increased chain-chain interactions, and these were enhanced in the presence of Na2 SO4. Galactose residues at different positions in xyloglucan oligosaccharides were hydrolysed at different rates. References. Albersheim P. (1976), Plant Biochemistry 3rd Ed. Bonner and Varner, Academic Press, de Silva J., Jarman CD., Stronach M., Arrowsmith D., Smith C, Sidebottom C, Reid J.S.G. (1993), Plant J. 1, 701-711. Edwards M,. Dea I.C.M., Bulpin P.V., Reid J.S.G. (1985), Planta 163, 133-140. Edwards M., Dea I.C.M., Bulpin P.V., Reid J.S.G. (1986), J. Biol. Chem. 261, 9489-9494. Edwards M., Dea I.C.M., Bulpin P.V., Reid J.S.G. (1988) J. Biol. Chem. 263, 4333-4337. Fanutti C., Gidley M.J., Reid J.S.G. (1991), Planta 184, 137-147. Fanutti C, Gidley M.J., Reid J.S.G. (1993), The Plant J. 3, 691-700. Fry S.C. (1989), J. Exp. Bot. 40, 1-11. Hayashi T. (1989), Annu. Rev. Plant Physiol. Plant Mol. Biol.40, 139-168.