PLANT PHYSIOLOGY , Vol 114, Issue 2 661-667, Copyright © 1997 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
A Xyloglucan-Specific Endo-1,4-[beta]-Glucanase Isolated from Auxin-Treated Pea Stems
T. Matsumoto, F. Sakai and T. Hayashi
Wood Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611 Japan
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
dodecyi 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->3,
1->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.