Trans-α-xylosidase, a widespread enzyme activity in plants, introduces (1→4)-α-d-xylobiose side-chains into xyloglucan structures

► Plant enzyme catalyses [3H]xylosyl transfer between xyloglucan oligosaccharides. ► Novel repeat-unit ('V') thus formed is identified as α-Xyl-(1,4)-α-Xyl-(1,6)-Glc. ► Highly sensitive methods developed for radiochemically characterising V. ► Eight xylose disaccharides, some not previously available, synthesised as markers. ► V units may affect oligosaccharin activity or xyloglucan's suitability as XET substrate.