An enzymatic signal amplification system for calorimetric studies of cellobiohydrolases

The study of cellulolytic enzymes has traditionally been carried out using endpoint measurements by quantitation of reaction products using high-performance liquid chromatography (HPLC) or overall determination of produced reducing ends. To measure catalytic activity, model substrates such as solubilized cellulose derivates, soluble chromogenic, and flourogenic oligomeric substrates are often employed even though they do not reflect the natural insoluble substrate hydrolysis. Thermochemical methods using, for example, isothermal titration calorimetry (ITC) yield data where the primary observable is heat production. This can be converted to the rate of reaction and allows direct and continuous monitoring of the hydrolysis of complex substrates. To overcome the low molar enthalpy of the hydrolysis of the glycosidic bond, which is typically on the order of −2.5 kJ mol−1, an enzymatic signal amplification method has been developed to measure even slow hydrolytically active enzymes such as cellobiohydrolases. This method is explained in detail for the amplification of the heat signal by more than 130 times by using glucose oxidase and catalase. The kinetics of this complex coupled reaction system is thoroughly investigated, and the potential use to generate kinetic models of enzymatic hydrolysis of unmodified cellulosic substrates is demonstrated.