Kinetics of the enzymatic hydrolysis of cellulose

Abstract

Enzymatic hydrolysis of cellulose for sugar production offers advantages of higher conversion, minimal by-product formation, low energy requirements, and mild operating conditions over other chemical conversions. The development of a kinetic model, based on observable, macroscopic properties of the overall system, is helpful in design and economic evaluation of processes for sugar conversion and ethanol production. A kinetic model is presented, incorporating enzyme adsorption, product inhibition, and considers a multiple enzyme and substrate system. This model was capable of simulating saccharification of a lignocellulosic material, rice straw, at high substrate (up to 333 g/L) and enzyme concentrations (up to 9.2 FPU/mL) that are common to proposed process designs.

Toward an aggregated understanding of enzymatic hydrolysis of cellulose: Noncomplexed cellulase systems

“…But Beltrame et al (1982) determined that the adsorption of protein consisted of irreversible steps, which were thought to arise from conformational changes of protein upon adsorption. Wald et al (1984) contradicted Beltrame's finding by reporting that adsorbed cellulase can be removed by washing with buffer. Using fractionated cellulase, Kyriacou et al (1989) found cellulase adsorption was irreversible, while Beldman et al (1987) found cellulase adsorption to be partially reversible.…”

“…Although such models have met with some success in terms of correlating data, the trend of increasing CrI with increasing conversion-which would be expected if amorphous cellulose in fact reacts first-has not been conclusively confirmed by experimental data. An example of a twosubstrate model is that of Wald et al (1984), which includes shrinking cellulose spheres with an amorphous shell and a shrinking core as well as inhibition of cellulose hydrolysis by cellobiose and liquid-phase hydrolysis of cellobiose by h-glucosidase with inhibition by glucose. South et al (1995) used a conversion-dependent rate constant to account for declining specific activity of cellulase -cellulose complexes over the course of hydrolysis:…”

“…Both the structural information Teeri et al, 1998a,b) and a considerable body of experimental data indicate that individual cellulase enzymes are inhibited Beltrame et al, 1982Langmuir Holtzapple et al, 1984aand b, 1990 Langmuir non-competitive Nakasaki et al, 1988M-M Steiner et al, 1988Langmuir Howell and Stuck, 1975 plus BG M-M Dwivedi and plus BG M-M competitive Ghosh et al, 1982 plus BG M-M competitive Asenjo, 1984 plus BG M-M competitive Caminal et al, 1985 plus BG M-M competitive Borchert and Buchholz, 1987 plus BG Langmuir competitive Guaskov and Sinitsyn, 1992 plus BG M-M non-competitive Moldes et al, 1999 plus BG M-M competitive Belkacemi and Hamoudi, 2003 plus BG M-M ii. Semimechanistic models with respect to enzyme only (>2 substrate state variables, 1 solubilizing activity) Converse and Grethlein, 1987 AS Peitersen and Ross, 1979 A + C plus BG M-M Fan and A + C plus BG Langmuir uncompetitive Scheiding et al, 1984 A + C plus BG Langmuir non-competitive Guaskov et al, 1985a and b A + C plus BG Langmuir competitive Gonzalez et al, 1989 A + C plus BG M-M competitive Nidetzky et al, 1993 A + C plus BG Langmuir Wald et al, 1984 AS + (A + C) plus BG Langmuir competitive Gan et al, 2003 AS + (A + C) plus BG Langmuir competitive iii. Semi mechanistic models with respect to substrate only (1 substrate state variable and 2 solubilizing activities) Beltrame et al, 1984 only [S] Endo+Exo+BG M-M non-competitive Nidetzky et al, 1994b only [S] Endo+Exo Langmuir C. Functionally based models (z2 substrate state variables, z2 solubilizing activities) Suga et al, 1975 [S], DP Endo+Exo M-M Okazaki and Moo-Young, 1978 [S], DP Endo+Exo M-M non-competitive Converse and Optekar, 1993 [S], AS Endo+Exo Dynamic adsorption Fenske et al, 1999 [S], AS, DP Endo+Exo Langmuir *AS = surface area; [S], substrate concentration; X = cellulose conversion; A, amorphous cellulose; C, crystalline cellulose.…”

Effect of potential binding site overlap to binding of cellulose to cellulose: a two‐dimensional simulation

“…Adsorption-based kinetic models for enzymatic cellulose hydrolysis have been developed [2,3] and the adsorption processes have also been studied in detail [4-71. Several equations, many of which are based on Langmuir adsorption theory, have been employed to describe these phenomena [&lo].…”

“…Several equations, many of which are based on Langmuir adsorption theory, have been employed to describe these phenomena [&lo]. The presence of two different types of substrates in cellulose which differ in their susceptibility to the binding of enzyme or enzymatic attack was proposed by Sattler et al [ 1 l] and Wald et al [12]. StLhlberg et al [13] showed that the experimental data fitted that type of model, but discussed the possibility of a broader 'continuous' affinity spectrum.…”