Optimized mixtures of recombinant Humicola insolens cellulases for the biodegradation of crystalline cellulose

The digestion of bacterial cellulose ribbons by ternary mixtures of enzymes consisting of recombinant cellulases (two cellobiohydrolases, Cel6A and Ce l7A, and the endoglucanase Ce145A) from Humicola insolens was investigated over a wide range of mixture composition. The extent of digestion was follo wed by soluble sugar release (saccharification) analysis together with tran smission electron microscopy (TEM) observations. It was found that the addi tion of minute quantities of Ce145A induced a spectacular increase in sacch arification of the substrate with either Cel7A or the mixture of Cel6A and Cel7A. Conversely, only a moderate saccharification resulted from the mixin g of Ce145A and Cel6A. This difference is believed to originate from (1) th e occasional endo character of Cel6A and (2) the competition of Cel6A and C e145A for the substrate sites that are sensitive to endo activity. Interest ingly, the mixture of enzymes giving rise to the highest saccharification r ate did not always correspond to mixtures of enzymes generating the highest synergy. TEM images revealed that the bacterial cellulose ribbons became a t the same time cut and narrowed down under the action of an optimized mixt ure of the three enzymes. (C) 2001 John Wiley & Sons, Inc.