Differences in catalytic properties between native isoenzymes of xyloglucan endotransglycosylase (XET)

• Published in: Phytochemistry (Oxford) Vol. 54; no. 7; pp. 667 - 680
• Main Authors: Steele, Nancy M, Fry, Stephen C
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Ltd 01-08-2000; Elsevier
• Subjects: Analytical, structural and metabolic biochemistry; Biological and medical sciences; Brassica oleracea var. botrytis; Catalysis; Cauliflower; Cell walls; Chromatography, Ion Exchange; Compositae; Enzymes; Enzymes and enzyme inhibitors; Fundamental and applied biological sciences. Psychology; Glycosyltransferases - metabolism; Hydrogen-Ion Concentration; Isoenzyme activity characterisation; Isoenzymes - metabolism; Leguminosae; Metabolism; Mung bean; Oligosaccharide; Plant physiology and development; Transferases; Transglycosylation; Vigna radiata; Xyloglucan; Xyloglucan endotransglycosylases; Brassica oleracea var. botrytis; Transglycosylation; Xyloglucan; Xyloglucan endotransglycosylases; Leguminosae; Cell walls; Oligosaccharide; Vigna radiata; Cauliflower; Compositae; Isoenzyme activity characterisation; Mung bean; Purification; Enzyme; Isozyme; Transferases; Glycosyltransferases; Pectin; Cell wall; Xyloglucan:xyloglucosyl transferase; Grain legume; Vegetable crop; Enzymatic activity; Cruciferae; Dicotyledones; Angiospermae; Hexosyltransferases; Spermatophyta; Kinetics; Optimum pH
• ISSN: 0031-9422; 1873-3700
• DOI: 10.1016/S0031-9422(00)00203-X

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),
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 μM) than the four mung bean isoenzymes (16–35 μM). 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.