Abstract
Cellulose microcrystals from the alga
Valonia macrophysa have been subjected to enzymatic degradation with purified cellulase components from the fungus
Trichoderma reesei. Electron microscopy reveals that 1,4-β-D-glucan cellobiohydrolase II erodes only one of the two tips of the microcrystals. This demonstrates not only the exo-action pattern of the enzyme, but also the parallel packing of the cellulose chains within
Valonia cellulose microcrystals. When 1,4-β-D-glucan cellobiohydrolase II is mixed with 1,4-β-D-glucan glucanohydrolase II, several sites of attack are observed, located at defects along the microcrystals. In that case again, the biodegradation is persistently unidirectional and visual evidence is given for the endo-exo co-operativity between the two enzymes.