PLANT PHYSIOLOGY , Vol 104, Issue 1 99-107, Copyright © 1994 by American Society of Plant Biologists
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METABOLISM AND ENZYMOLOGY |
The Effect of Xyloglucans on the Degradation of Cell-Wall-Embedded Cellulose by the Combined Action of Cellobiohydrolase and Endoglucanases from Trichoderma viride
J. P. Vincken, G. Beldman and AGJ. Voragen
Wageningen Agricultural University, Department of Food Science, 6700 EV Wageningen, The Netherlands
Two endoglucanases of Trichoderma viride, endoI and endoIV, were assayed
for their activity toward alkali-extracted apple xyloglucans. EndoIV was
shown to have a 60-fold higher activity toward xyloglucan than endoI,
whereas carboxymethyl cellulose and crystalline cellulose were better
substrates for the latter. The enzymic degradation of cellulose embedded in
the complex cell-wall matrix of apple fruit tissue has been studied using
cellobiohydrolase (CBH) and these two different endoglucanases. A
high-performance liquid chromatographic method (Aminex HPX-22H) was used to
monitor the release of cellobiose and oligomeric xyloglucan fragments.
Synergistic action between CBH and endoglucanases on cell-wall-embedded
cellulose was, with respect to their optimal ratio, slightly different from
that reported for crystalline cellulose. The combination of endoIV and CBH
solubilized twice as much cellobiose compared to a combination of endoI and
CBH. Apparently, the concomitant removal of the xyloglucan coating from
cellulose microfibrils by endoIV is essential for an efficient degradation
of cellulose in a complex matrix. Cellulose degradation slightly enhanced
the solubilization of xyloglucans. These results indicate optimal
degradation of cell-wall-embedded cellulose by a three-enzyme system
consisting of an endoglucanase with high affinity toward cellulose (endoI),
a xyloglucanase (endoIV), and CBH.