Effects of Primary Hydroxyl Groups and Reducing Ends Alteration on Cellulose-Cellulase Interactions and Cellulose Hydrolysis

In contrast to the findings of Xu et al. (2009), we previously reported that alteration of cellulose reducing ends by reduction with sodium borohydride (NaBH₄) and oxidation with bicinchoninic acid (BCA) or acetic acid catalyzed sodium chlorite (SC/AA) had insignificant impact on cellulose hydrolysis rates and final conversions mediated with complete cellulase; as well as purified cellulase components (Kumar et al., 2014). It was also reported that SC/AA possibly altered the primary hydroxyl groups (PHGs) of cellulose to the glucuronic acid moiety, which had detrimental impact on cellulose hydrolysis, especially at low cellulase loadings. However, it was not clear whether or not the reduction in cellulose conversion following SC/AA treatment was due to PHG oxidation. In this study, our goal was to understand the implications of alteration of the primary hydroxyl groups and reducing ends in the context of cellulose-cellulase action and cellulose hydrolysis. We used complete cellulase systems; as well as purified cellulase components to conduct this work. PHG alteration was performed on untreated and NaBH₄ reduced Avicel® PH101 cellulose by applying the standard 2, 2, 6, 6-tetramethylpiperidine-1-oxyl radical (TEMPO) mediated sodium hypochlorite oxidation (Saito and Isogai, 2004). Adsorption isotherms and adsorption equilibria for complete cellulase formulations; as well as purified cellobiohydrolase I (Cel7A), were determined. Work was conducted at both 4°C and at 50°C to better understand the impact of cellulose reducing ends and alteration of PHGs on cellulose-cellulase interactions and cellulose hydrolysis, respectively.