THE EFFECT OF XYLOGLUCANS ON THE DEGRADATION OF CELL-WALL-EMBEDDED CELLULOSE BY THE COMBINED ACTION OF CELLOBIOHYDROLASE AND ENDOGLUCANASES FROM TRICHODERMA-VIRIDE

Two endoglucanases of Trichoderma viride, endol and endolV, were assayed for their activity toward alkali-extraded apple xyloglucans. EndolV was shown to have a 60-fold higher activity toward xyloglucan than endol, 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 endolV and CBH solubilized twice as much cellobiose compared to a combination of endol and CBH. Apparently, the concomitant removal of the xyloglucan coating from cellulose microfibrils by endolV 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 (endol), a xyloglucanase (endolV), and CBH.