Kinetics of fungal cellulases

Cellulose, a linear, essentially insoluble 8-1,4glucosidically linked polymer with a size of many thousand glucose units, is one of the main components of plant materials. Many micro-organisms can degrade this polymer; they produce many different cellulases which differ in both their mode of action and their overall folds. Fungal organisms which degrade cellulose produce many different cellulases which can be classified into families according to their sequences [ 13. The saprophytic fungus Humicola insolens produces seven different cellulases which belong to five different families (family 5, 6, 7, 12 and 45); it produces one endoglucanase (EG) from each family and two cellobiohydrolases (CBH) from two different families (6 and 7) [2,3]. One of the best characterized cellulolytic fungi, Trichodema reesei, produces at least six cellulases [4]. The catalytic activity of cellulases can be determined by many different methods. However, the real substrate, cellulose, is heterogeneous and contains both amorphous and crystalline areas; the cellulases will have different reaction rates depending on which part of the structure they degrade. The cellulose binding domain (CBD) present in many cellulases can also result in non-productive binding. For accurate kinetic determinations, the ideal substrate should be soluble; for enzymatic characterization of fungal cellulases, soluble cellohexaitol and carboxy methyl cellulose (CMC) have been used. For obtaining information on the apparent kinetics of an insoluble substrate, the insoluble phosphoric acid swollen cellulose (PASC) was chosen as the most amorphous and homogeneous cellulose. The activity of the cellulase on the different