ACTION OF A PURE XYLOGLUCAN ENDO-TRANSGLYCOSYLASE (FORMERLY CALLED XYLOGLUCAN-SPECIFIC ENDO-(1-]4)-BETA-D-GLUCANASE) FROM THE COTYLEDONS OFGERMINATED NASTURTIUM SEEDS

The action on tamarind seed xyloglucan of the pure, xyloglucan-specifi c endo-(1-->4)-beta-D-glucanase from nasturtium (Tropaeolum majus L.) cotyledons has been compared with that of a pure endo-(l-->)-beta-D-gl ucanase ('cellulase') of fungal origin. The fungal enzyme hydrolysed t he polysaccharide almost completely to a mixture of the four xylogluca n oligosaccharides: [GRAPHICS] Exhaustive digestion with the nasturtiu m enzyme gave the same four oligosaccharides plus large amounts of hig her oligosaccharides and higher-polymeric material. Five of the produc t oligosaccharides (D,E,F,G,H) were purified and shown to be dimers of oligosaccharides A to C. D (glc8xyl6) had the structure A-->A, H (glc 8xyl6gal4) was C-->C, whereas E (glc8xyl6gal), F (glc8xYl6gal2) and G (glc8xyl6gal3) were mixtures of structural isomers with the appropriat e composition. For example, F contained B2-->B2 (30%), A-->C (30%), C- ->A (20%), B2-B1 (15%) and others (about 5%). At moderate concentratio n (about 3 mM) oligosaccharides D to H were not further hydrolysed by the nasturtium enzyme, but underwent transglycosylation to give oligos accharides from the group A, B, C, plus higher oligomeric structures. At lower substrate concentrations, hydrolysis was observed. Similarly, tamarind seed xyloglucan was hydrolysed to a greater extent at lower concentrations. It is concluded that the xyloglucan-specific nasturtiu m-seed endo-(1-4)-beta-D-glucanase has a powerful xyloglucan-xylogluca n endo-transglycosylase activity in addition to its known xyloglucan-s pecific hydrolytic action. It would be more appropriately classified a s a xyloglucan endo-transglycosylase. The action and specificity of th e nasturtium enzyme are discussed in the context of xyloglucan metabol ism in the cell walls of seeds and in other plant tissues.