Abstract
Xyloglucan endotransglucosylases (XETs) catalyze the transfer of a portion from a donor xyloglucan to another xyloglucan molecule, and are considered to contribute to the loosening or rigidity of the cell wall, because xyloglucans cross-link adjacent cellulose microfibrils. To identify and define the reaction mechanism of XETs, we purified XET isoenzymes from growing pea stems. Five XETs were obtained by sequential lectin affinity chromatography, gel permeation chromatography, cation exchange chromatography, and chromatofocusing. The pI values (with molecular masses) of purified five enzymes were 7.8 (31 kDa), 7.1 (29 kDa), 7.0 (31 kDa), 6.8 (29 kDa) and 6.5 (29 kDa), respectively. All the enzymes showed a transferase activity but no hydrolase activity for xyloglucans. These isoenzymes have different pH optima (range 5.5-7.0). They were highly specific for xyloglucans, and showed no transglucosylation activity for other glucans and xylans.
