A xyloglucan-oligosaccharide-specific α-d-xylosidase or exo-oligoxyloglucan-α-xylohydrolase from germinated nasturtium (Tropaeolum majus L.) seeds : Purification, properties and its interaction with a xyloglucan-specific eneto-(1→4)-β-d-glucanase and other hydrolases during storage-xyloglucan mobilisation

Abstract

The α-xylosidase which is involved in the postgerminative mobilisation of xyloglucan in nasturtium seed cotyledons has now been purified to apparent homogeneity by a facile procedure involving lectin affinity chromatography. The purified enzyme, a glycoprotein, moved as a single band (apparent molecular weight 85000) on sodium dodecyl sulphate-gel electrophoresis, whilst isoelectric focusing gave a number of enzymatically active protein bands spanning the range pI = 5.0 to 7.1 (maximum activity at pI = 6.1). The enzyme did not hydrolyse the simple α-xylosides p-nitrophenyl-α-d-xylopyranoside and woprimeverose (α-d-Xyl(1→6)-d-Glc), or polymeric tamarind-seed xyloglucan. It released xylose from a complex mixture of oligosaccharides produced by exhaustive hydrolysis of tamarind seed xyloglucan using the xyloglucan-specific endo-(1→4)-β-d-glucanase from germinated nasturtium seeds (M. Edwards et al. 1986, J. Biol. Chem., 261. 9489-9494). The three xyloglucan oligosaccharides of lowest molecular size were purified from this mixture and were shown by (1)H-nuclear magnetic resonance ((1)H-NMR) and enzymatic analysis to have the structures: