Cellulose from the gram-negative bacterium
Acetobacter xylinum has been used as a model substrate
for visualizing the action of cellulase enzymes from the fungus
Trichoderma reesei. Enzymes are initially observed bound
to the cellulose ribbon. Within 10 min, the ribbon is split along
its long axis into bundles of microfibrils which are subsequently
thinned until they are completely dissolved within 30 min. Incubations
with purified components of the cellulase enzyme system produced
less dramatic changes in ribbon structure. Purified 1,4--D-glucan
cellobiohydrolase produced no visible change in cellulose structure.
Purified endo-1,4--D-glucanase produced some splaying of ribbons
into microfibril bundles. In both cases, whole ribbons were present
even after 60 min of incubation, visually confirming the synergistic
mode of action of these enzymes.