Differences in catalytic properties between native isoenzymes of xyloglucan endotransglycosylase (XET).
Four isoenzymes of xyloglucan endotransglycosylase (XET; EC 2.4.1.207) 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), Km for the nonasaccharide XLLGol (Gal2.Xyl3.Glc3.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 Km values for XLLGol (70-130 microM) than the four mung bean isoenzymes (16-35 microM). 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.
Steele
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The Edinburgh Cell Wall Group, Institute of Cell and Molecular Biology, The University of Edinburgh, UK.
Fry
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D002384:Catalysis; D002852:Chromatography, Ion Exchange; D016695:Glycosyltransferases / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000378:metabolism*
D007527:Isoenzymes; D016695:Glycosyltransferases; C073693:xyloglucan endotransglycosylase