SUBSTRATE-SPECIFICITY OF ENDOGLUCANASES - WHAT DETERMINES XYLOGLUCANASE ACTIVITY

Endoglucanases from Trichoderma viride differ in their activity and mo de of action towards xyloglucans. In order to explain the basis for th eir different behavior, the number of substrate-binding sites of three endoglucanases (endoI, endoIV, and endoV) were determined using bond cleavage frequencies of both normal and reduced cellodextrins and k(o) /K-m. EndoIV differed from other endoglucanases described so far, in h aving at least nine putative binding sites. The specificities of the t hree endoglucanases towards various xyloglucans derived from apple fru it and potato were determined. Also, the release of oligosaccharides f rom these substrates in time was monitored. It was concluded that the endoglucanases prefer to bind unbranched glucosyl residues. Because mo st xyloglucans are composed of XXXG-type of building units, distant su bsites are needed to bind xyloglucan. Having at least nine substrate-b inding sites, endoIV seems to be well equipped to degrade xyloglucans which was confirmed by its high xyloglucanase activity. (C) 1997 Elsev ier Science Ltd.