Effects of Sugar Inhibition on Cellulases and β-Glucosidase During Enzymatic Hydrolysis of Softwood Substrates

Abstract

A quantitative approach was taken to determine the inhibition effects of glucose and other sugar monomers during cellulase and beta-Glucosidase hydrolysis of two types of cellulosic material: Avicel and acetic acid-pretreated softwood. The increased glucose content in the hydrolysate resulted in a dramatic increase in the degrees of inhibition on both beta-Glucosidase and cellulase activities. Supplementation of mannose, xylose, and galactose during cellobiose hydrolysis did not show any inhibitory effects on beta-Glucosidase activity. However, these sugars were shown to have significant inhibitory effects on cellulase activity during cellulose hydrolysis. Our study suggests that high-substrate consistency hydrolysis with supplementation of hemicellulose is likely to be a practical solution to minimizing end-product inhibition effects while producing hydrolysate with high glucose concentration.

Transforming biomass conversion with ionic liquids: process intensification and the development of a high-gravity, one-pot process for the production of cellulosic ethanol

“…It is also worth mentioning that endproduct inhibition (e.g., concentrated glucose and cellobiose) could affect the enzyme activity and further lower glucose yield. 13 Simultaneous saccharification and fermentation was thus incorporated into the one-pot system to improve the overall yield of glucose as well as ethanol.…”

“…However, there remain engineering challenges that must be addressed before HG biomass processing could be applied using the one-pot process approach. These challenges include: 1) The mass transfer limitation that exists throughout pretreatment, saccharification, and fermentation unit operations due to the water constraint; 2) The generation of inhibitory products at high solid loading is expected and could pose problems for downstream processing, 12 and concentrated end-products (e.g., glucose, cellobiose) may decrease overall enzyme activity; 13 3)…”

Biological processing in oscillatory baffled reactors: operation, advantages and potential

“…During the enzymatic conversion of cellulose into monosaccharide, cellulase deactivation occurs. This deactivation of cellulases is caused by a number of process-dependent factors: shear inactivation [45][46][47][48], sugar inhibition [86], ion strength [87], temperature [88] and formation of inert enzyme substrate complexes. A further factor involved in cellulose depolymerization is the changing nature of the substrate over time; the easily hydrolysable amorphous regions are digested first leaving the recalcitrant crystalline regions [89].…”

Origin of Initial Burst in Activity for Trichoderma reesei endo-Glucanases Hydrolyzing Insoluble Cellulose

“…This behavior is of particular interest both in attempts to elucidate the molecular mechanisms and regulation of cellulolytic enzymes and in the application of cellulases for the industrial breakdown of biomass. Thus, a typical biomass saccharification starts with a conversion of up to 50% in the first 24 h but takes 2-5 days to achieve appreciable yields (Ͼ80%) of glucose (9). For the breakdown of complex biomass the slowdown is undoubtedly controlled by a variety of factors, but the observation of a distinct burst and slowdown for pure cellulose/cellulase systems at very low degrees of conversion has directed the focus to the intrinsic molecular properties of the enzymes and substrate (10 -14).…”