Kinetics and mathematical model of hydrolysis and transglycosylation catalysed by cellobiase

Abstract

The kinetics of hydrolysis and transglycosylation reactions catalysed by cellobiase (β- d-glucoside glucohydrolase, EC 3.2.1.21) from Aspergillus foetidus in the cellobiose- d-glucose reaction system have been studied. The formation of transglycosylation products was observed at cellobiose concentrations >10 −2 m , whereas at lower substrate concentrations the only reaction product was d-glucose. In the cellobiase-catalysed transglycosylation a (1→6)-β-linkage was formed after the transfer of a d-glucose residue to acceptor molecule. The basic transglycosylation products were isocellotriose and gentiobiose. A small amount of oligosaccharides with a higher degree of polymerization was also formed. The maximum content of transglycosylation products amounted to 25–30% of the total saccharide content in the system at the initial cellobiose concentration (0.1–0.3 m). The processes in the reaction system were inhibited by the substrate and product ( d-glucose). A general scheme for cellobiose hydrolysis has been proposed and validated, allowing for the inhibition and transglycosylation effects. Based on this scheme, a mathematical model for cellobiose hydrolysis has been suggested to describe the kinetics of substrate consumption and product ( d-glucose) accumulation, as well as the kinetics of formation and consumption of transglycosylation products throughout the course of enzymatic reaction with various initial amounts of cellobiose, starting from low concentrations up to 0.2–0.3 m (7–11% bv weight).