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A xyloglucan-specific endo-1,4-beta-glucanase isolated from auxin-treated pea stems

Matsumoto, T., Sakai, F., Hayashi, T.
Plant physiology 1997 v.114 no.2 pp. 661-667
metabolism, stems, xyloglucans, cellulases, beta-glucanase, auxins, chemical constituents of plants, Pisum sativum, protein content, enzyme activity
A xyloglucan-specific endo-1,4-beta-glucanase was isolated from the apoplast fraction of auxin-treated pea (Pisum sativum) stems, in which both the rate of stem elongation and the amount of xyloglucan solubilized were high. The enzyme was purified to apparent homogeneity by sequential cation-exchange chromatographies, affinity chromatography, and gel filtration. The purified enzyme gave a single protein band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and the molecular size was determined to be 77 kD by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and 70 kD by gel filtration. The isoelectric point was about 8.1. The enzyme specifically cleaved the 1,4-beta-glucosyl linkages of the xyloglucan backbone to yield mainly nona- and heptasaccharides but did not hydrolyze carboxymethylcellulose, swollen cellulose, and (1 leads to 3, 1 leads to 4)-beta-glucan. By hydrolysis, the average molecular size of xyloglucan was decreased from 50 to 20 kD with new reducing chain ends in the lower molecular size fractions. This suggests that the enzyme has endo-1,4-beta-glucanase activity against xyloglucan. In conclusion, a xyloglucan-specific endo-1,4-beta-glucanase with an activity that differs from the activities of cellulase and xyloglucan endotransglycosylase has been isolated from elongating pea stems.