Characterization of a cellodextrin glucohydrolase with soluble oligomeric substrates: experimental results and...

A previously isolated cellodextrin glucohydrolase (beta-glucosidase) from Trichoderma reesei QM 9414 is characterized using beta-1,4-glucose oligomers with defined degrees of polymerization as soluble substrates. The enzyme splits off glucose units from the nonreducing chain ends of cellooligomers. Besides this hydrolytic activity there is also evidence for transfer activity depending on the concentration and degree of polymerization of substrates. Concentration-time-course data have been gathered for the degradation of cellobiose, cellotriose, cellotetraose, cellopentaose, and cellohexaose covering a wide range of enzyme and substrate concentrations. A Michaelis-Menten type kinetic model has been developed, which is able to satisfactorily describe the complex system of parallel and series reactions during the conversion of oligomers to glucose. The only kind of inhibition considered is competitive inhibition by the final product glucose. The model takes into account the formation of multiple enzyme-substrate complexes and is limited to those conditions, in which no transglucosylation products are observed. Cellodextrins with higher degrees of polymerization are found to be better substrates for this enzyme than is the dimer cellobiose.