(10d) Inhibition of ENZYMATIC Hydrolysis by Soluble Sugars ON MODEL CELLULOSE Thin Film USING QUARTZ CRYSTAL Microbalance

 Hsin-Fen Li ¹, Ravinder Garlapalli¹.  Michael D. Flythe ^2,3, Sue E. Nokes ⁴, Stephen E. Rankin¹, Barbara L. Knutson¹

¹University of Kentucky, Department of Chemical and Materials Engineering, Lexington, Kentucky 40506

²USDA, Agricultural Research Service, Forage-Animal Production Research Unit; Lexington, Kentucky 40546

³University of Kentucky, Department of Animal and Food Sciences, Lexington, Kentucky 40546

⁴University of Kentucky, Department of Biosystems and Agricultural Engineering, Lexington, Kentucky 40506

Soluble sugars produced from the hydrolysis of cellulose are one of the most promising feedstocks for production of fuels and commodity chemicals from renewable plant-based resources. The recalcitrance of cellulose to degradation is well documented and attributed to multiple sources, including high cellulose crystallinity and the hydrogen binding framework that is embedded in the matrix substances (lignin and hemicellulose).  Cellulase is a cellulytic enzyme that possess a catalytic domain capable of hydrolyzing the beta-1, 4-glycosidic bonds in cellulose.  However, during biomass conversion to soluble sugars, its hydrolytic efficiency is limited by the presence of degradation products including cellobiose.  To study the inhibitory effect of cellobiose and the interaction of the inhibited enzyme and the cellulose substrate, the change in mass and surface properties of cellulose thin films were measured using Quartz Crystal Microbalance with Dissipation (QCM-D).  The cellulose thin film was synthesized from thermochemically dissolved cellulose and was coated on a quartz crystal resonator.  The mass of the spin-coated cellulose film was detected by the resonance frequency, and the cellulose surface coverage was observed by atomic force microscopy (AFM).  Cellulase adsorption, activity, and inhibition on model cellulose thin films as were measured directly as changes to the piezoelectric properties of the cellulose thin films by QCM-D.  At 5 g/L, cellobiose completely inhibits cellulase (0.5 %v/v) activity.  The inhibited cellulases bind reversibly to the cellulose and reduce subsequent enzymatic hydrolysis rates by more than 50%.  Significantly higher activity is observed when cellulase concentration is decreased from 1 %v/v to 0.1 %v/v, suggesting that cellulase acts progressively on the cellulose chain, and the hydrolysis is restricted by saturated enzyme conditions.