Differential effects of inorganic salts on cellulase kinetics in enzymatic saccharification of cellulose and lignocellulosic biomass

Abstract

Inorganic salt pretreatment of lignocellulosic biomass has proven to be an efficient way to increase the efficiency of enzymatic saccharification. However, it is not clear that this improvement is the result of modification of the lignocellulosic substrate after pretreatment, or removal of inhibitor, or enhancement of cellulase or a combination of these events. Therefore, this study aimed to analyze the effects of inorganic salts on kinetics of cellulase enzymes (celluclast 1.5L and accellerase 1500). Two substrates rich in cellulose content [carboxymethylcellulose (CMC), avicel (AV)] and lignocellulose substrate [sugarcane bagasse (SB)] were considered. The enzymatic saccharification was carried with and without the addition of inorganic salts (NaCl and KCl) at 0.5 M and 1.0 M concentration. The kinetic parameters, Km and Vm, were determined to mechanically understand the pattern of inhibition and enhancement of inorganic salts on enzymatic saccharification. The kinetics parameters of celluclast 1.5L and accellerase 1500 for hydrolysis of CMC and AV with NaCl showed uncompetitive inhibition. Whereas, influences of KCl on both cellulase were differentiated to function in inhibition or enhancement modes when challenged with different substrates. On the other hand, enzymatic hydrolysis efficiencies of SB using both cellulases were enhanced under addition of NaCl and KCl, by increasing Vm of celluclast 1.5L from 0.303 to 0.635 mg/mL min (0.5 M KCl) and accellerase 1500 from 0.383 to 0.719 mg/mL min (1.0 M NaCl). The details of kinetic analysis in this work revealed the mechanism of inorganic salts on cellulase kinetics to be involved in substrate modification and removal of inhibitor. Graphic abstract: [Figure not available: see fulltext.] © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.