NARA investigates conversion technologies that rely on enzymes called cellulases. Cellulases break down the cellulose and hemicellulose polymers found in wood and release simple sugars. The simple sugars can then be used to make isobutanol and other valued chemical products.
Recently, it was observed that cellulases work better when lignosulfonates are present (Wang et al. 2013; Zhou et al, 2013). These findings are interesting because before the cellulase enzyme can begin cleaving off simple sugars, the lignin around the cellulase needs to be partially removed through a process called pretreatment; however, adding sulfonated lignin to the reaction makes the cellulase enzyme work better.
To better understand this relationship, NARA researcher J.Y Zhu and his team investigated the interaction of lignin, cellulose and cellulase and published their results in Understanding the effects of lignosulfonates on enzyme saccharification of pure cellulose.
Read Understanding the effects of lignosulfonates on enzyme saccharification of pure cellulose here.
Effect on cellulase depends on lignosulfonate concentration
First, they wanted to know how much lignosulfonate was needed to affect the cellulase activity. Here they discovered that under very dilute concentrations of lignosulfonates, cellulase activity actually decreased. As lignosulfonate concentrations increased, cellulase activity was enhanced.
So what is going on? The authors suggest that lignosulfonates can bind to cellulases and interfere with their ability to perform their cleaving function. This explains how low concentrations of lignosulfonates inhibit cellulase activity. At higher concentrations, however, the authors suggest that lignosulfonates act as a surfactant. They bind to the cellulase to help stabilize the enzyme and enhance its binding to the cellulose. Adding 5 grams/liter of lignosulfonates increased enzyme efficiency by 20%.
Lignosulfonates act as a surfactant
To verify this conclusion, they evaluate how different sized lignosufonates, number of sulfur groups attached to the lignin, ionic strength and pH affect cellulase activity. The results from these experiments reinforced the surfactant theory and suggest that smaller lignosulfonates with high amounts of sulfonation work best.
Lignosulfonates have traditionally been used as surfactants to bind dust, condition soil, and disperse concrete. Their use to enhance cellulase activity is appealing because lignosulfonates are relatively inexpensive, abundant, and they are a byproduct of the sulfite-based pretreatment strategy proposed for the conversion of forest residuals to biojet fuel.
References
Wang Z, Zhu JY, Fu Y, Qin M, Shao Z, Jiang J, Yang F (2013) Lignosulfonate-mediated cellulase adsorption: enhanced enzymatic saccharification of lignocellulose through weakening nonproductive binding to lignin. Biotechnol Biofuels 6:156
Zhou H, Lou H, Yang D, Zhu JY, Qiu X (2013) Lignosulfonate to enhance enzymatic saccharification of lignocelluloses: Role of molecular weight and substrate lignin. Ind Eng Chem Res 52(25):8464–8470