Four isoenzymes of xyloglucan endotransglycosylase (XET; EC 22.214.171.124) were isolated from sprouting mung bean seedlings (M35, M45, M55a, M55b) and two from cauliflower florets (C30, C45). Purification in each case was by ammonium sulphate precipitation, reversible formation of a covalent xyloglucan-enzyme complex, and cation-exchange chromatography. The isoenzymes differed in pH optimum (range 5.0-6.5), K-m for the nonasaccharide XLLGol (Gal(2).Xyl(3).Glc(3).glucitol) as acceptor substrate, ability to utilise diverse oligosaccharides as acceptor substrate, and ability to bind to carboxymethyl-cellulose (and thus possibly to other polyanions such as pectin in the cell wall). None of the isoenzymes was particularly cold-tolerant, unlike one XET (TCH4) of Arabidopsis. The two cauliflower isoenzymes had higher K-m values for XLLGol (70-130 mu M) than the four mung bean isoenzymes (16-35 mu M). We suggest that this difference is related to the major roles of the XETs in these two tissues: integration of new xyloglucan into the walls of the densely cytoplasmic cauliflower florets, and re-structuring of existing wall material in the rapidly vacuolating bean shoots. (C) 2000 Elsevier Science Ltd. All rights reserved.
|Number of pages||14|
|Publication status||Published - Aug 2000|