Zheng Wenqiu, Lan Tianqing, Li Hui, Yue Guojun, Zhou Haifeng
1Faculty of Agriculture and Food, Kunming University of Science and Technology, 727 South Jingming Rd, Chenggong District, Kunming, 650500 China.
2State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, No. 381 Wushan Rd, Guangzhou, 510640 China.
Biotechnol Biofuels. 2020 Jan 30;13:19. doi: 10.1186/s13068-020-1659-5. eCollection 2020.
Cellulase adsorbed on cellulose is productive and helpful to produce reducing sugars in enzymatic hydrolysis of lignocellulose; however, cellulase adsorbed on lignin is non-productive. Increasing productive adsorption of cellulase on cellulose would be beneficial in improving enzymatic hydrolysis. Adding lignin that was more hydrophilic in hydrolysis system could increase productive adsorption and promote hydrolysis. However, the effect mechanism is still worth exploring further. In this study, lignosulfonate (LS), a type of hydrophilic lignin, was used to study its effect on cellulosic hydrolysis.
The effect of LS on the enzymatic hydrolysis of pure cellulose (Avicel) and lignocellulose [dilute acid (DA) treated sugarcane bagasse (SCB)] was investigated by analyzing enzymatic hydrolysis efficiency, productive and non-productive cellulase adsorptions, zeta potential and particle size distribution of substrates. The result showed that after adding LS, the productive cellulase adsorption on Avicel reduced. Adding LS to Avicel suspension could form the Avicel-LS complexes. The particles were charged more negatively and the average particle size was smaller than Avicel before adding LS. In addition, adding LS to cellulase solution formed the LS-cellulase complexes. For DA-SCB, adding LS decreased the non-productive cellulase adsorption on DA-SCB from 3.92 to 2.99 mg/g lignin and increased the productive adsorption of cellulase on DA-SCB from 2.00 to 3.44 mg/g cellulose. Besides, the addition of LS promoted the formation of LS-lignin complexes and LS-cellulase complexes, and the complexes had more negative charges and smaller average sizes than DA-SCB lignin and cellulase particles before adding LS.
In this study, LS inhibited Avicel's hydrolysis, but enhanced DA-SCB's hydrolysis. This stemmed from the fact that LS could bind cellulase and Avicel, and occupied the binding sites of cellulase and Avicel. Thus, a decreased productive adsorption of cellulase on Avicel arose. Regarding DA-SCB, adding LS, which enhanced hydrolysis efficiency of DA-SCB, increased the electrostatic repulsion between DA-SCB lignin and cellulase, and therefore, decreased non-productive adsorption of cellulase on DA-SCB lignin and enhanced productive adsorption of cellulase on DA-SCB cellulose.
吸附在纤维素上的纤维素酶具有活性，有助于木质纤维素的酶水解过程中产生还原糖；然而，吸附在木质素上的纤维素酶则无活性。提高纤维素酶在纤维素上的活性吸附量将有利于改善酶水解效果。在水解体系中添加亲水性更强的木质素可以增加活性吸附并促进水解。然而，其作用机制仍值得进一步探索。在本研究中，使用木质素磺酸盐（LS）这种亲水性木质素来研究其对纤维素水解的影响。
通过分析酶水解效率、活性和非活性纤维素酶吸附量、底物的zeta电位和粒径分布，研究了LS对纯纤维素（微晶纤维素）和木质纤维素[稀酸（DA）处理的甘蔗渣（SCB）]酶水解的影响。结果表明，添加LS后，纤维素酶在微晶纤维素上的活性吸附量降低。向微晶纤维素悬浮液中添加LS可形成微晶纤维素-LS复合物。这些颗粒带负电荷更多，且平均粒径比添加LS前的微晶纤维素更小。此外，向纤维素酶溶液中添加LS可形成LS-纤维素酶复合物。对于DA-SCB，添加LS使纤维素酶在DA-SCB上的非活性吸附量从3.92 mg/g木质素降至2.99 mg/g木质素，并使纤维素酶在DA-SCB上的活性吸附量从2.00 mg/g纤维素增加到3.44 mg/g纤维素。此外，LS的添加促进了LS-木质素复合物和LS-纤维素酶复合物的形成，且这些复合物比添加LS前的DA-SCB木质素和纤维素酶颗粒带更多负电荷且平均粒径更小。
在本研究中，LS抑制了微晶纤维素的水解，但增强了DA-SCB的水解。这是因为LS可结合纤维素酶和微晶纤维素，并占据了纤维素酶与微晶纤维素的结合位点。因此，纤维素酶在微晶纤维素上的活性吸附量降低。对于DA-SCB，添加LS提高了DA-SCB的水解效率，增加了DA-SCB木质素与纤维素酶之间的静电排斥力，从而减少了纤维素酶在DA-SCB木质素上的非活性吸附，并增强了纤维素酶在DA-SCB纤维素上的活性吸附。
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