Properties and performance of glucoamylases for fuel ethanol production

Studies were conducted on maltodextrin saccharification and on simultaneous saccharification and fermentation (SSF) with various commercial glucoamylases. In kinetics studies, none of the glucoamylases were able to completely convert maltodextrin into glucose. Typically, about 85% conversion was obtained, and glucose yields were about 75%. Typically, the kinetics were biphasic, with 1 h of rapid conversion, then a significant reduction in rate. Data were consistent with strong product inhibition and/or enzyme inactivation. Some glucoamylases followed first-order kinetics, initially slower at dextrin conversion, but eventually achieving comparable conversion and glucose concentrations. Most of the glucoamylases were more active at 55°C than at 35°C, but pH had little effect on activity. Screening studies in an SSF system demonstrated little difference between the glucoamylases, with a few exceptions. Subsequent targeted studies showed clear differences in performance, depending on the fermentation temperature and yeast used, suggesting that these are key parameters that would guide the selection of a glucoamylase.     

Immobilization of Glucoamylase onto Novel Porous Supports Containing Cyclic Carbonate

Usually, before enzyme was immobilized onto support materials, these support materials had been activated through some activators, such as glutaraldehyde. The glucoamylase has been covalently immobilized onto several different support materials through the formation of Schiff base1-5. In this work, the glucoamylase was covalently (in the form of σ-bond) immobilized onto the porous polymer supports containing cyclic carbonate without activation. The relationship between the activity of the …     

Study on the Activity and Kinetic Characteristics of Glucoamylase in W/O Microemulsion Systems

The activity and kinetic characteristics of glucoamylase has been investigated in W/0 microemulsion systems of AOT/isooctane/buffer, CTAB/isooctane/l-pentanol/buffer and TX-100/ibooctane/I-pentanol/buffer, and compared with that in aquous solution. The effect of various parameters, such as pH optimum, To ptimum and water content, on the activity of the enzyme in microemulsion was determined. The results obtained show that the structure of the microemulsion has strong effect on enzyme activity compared to the k_cat, in aquous solution, the apparent turnover number k'_cat values were decreased in AOT, TX- 100 based system, and in creased in CTAB based system.     

Continuous Production of Ethanol from Starch Using Glucoamylase and Yeast Co-Immobilized in Pectin Gel

This work presents a continuous simultaneous saccharification and fermentation (SSF) process to produce ethanol from starch using glucoamylase and Saccharomyces cerevisiae co-immobilized in pectin gel. The enzyme was immobilized on macroporous silica, after silanization and activation of the support with glutaraldehyde. The silica–enzyme derivative was co-immobilized with yeast in pectin gel. This biocatalyst was used to produce ethanol from liquefied manioc root flour syrup, in three fixed bed reactors. The initial reactor yeast load was 0.05 g wet yeast/ml of reactor (0.1 g wet yeast/g gel), used in all SSF experiments. The enzyme concentration in the reactor was defined by running SSF batch assays, using different amount of silica–enzyme derivative, co-immobilized with yeast in pectin gel. The chosen reactor enzyme concentration, 3.77 U/ml, allowed fermentation to be the rate-limiting step in the batch experiment. In this condition, using initial substrate concentration of 166.0 g/l of total reducing sugars (TRS), 1 ml gel/1 ml of medium, ethanol productivity of 8.3 g/l/h was achieved, for total conversion of starch to ethanol and 91% of the theoretical yield. In the continuous runs, feeding 163.0 g/l of TRS and using the same enzyme and yeast concentrations used in the batch run, ethanol productivity was 5.9 g ethanol/l/h, with 97% of substrate conversion and 81% of the ethanol theoretical yield. Diffusion effects in the extra-biocatalyst film seemed to be reduced when operating at superficial velocities above 3.7 × 10⁻⁴ cm/s.     

葡萄糖苷酶抑制剂作用机理的分子动力学模拟和自由能计算

含有锍离子的葡萄糖苷酶抑制剂如kotalanol (SK)和它除去磺酸基团后的衍生物(DSK), 是潜在的毒副作用较小的治疗II 型糖尿病的候选药物. α-葡萄糖苷酶抑制活性实验显示, DSK活性比SK略高, 而将二者环上的S原子替换成NH后(分别称为DSN和SN), DSN的活性要比SN高1500倍左右. 本文用分子动力学模拟, 结合自由能计算和自由能分解的方法对上述四个抑制剂的作用机理进行了研究. 研究结果表明活性的巨大差异是由NH基团取代效应和磺酸基团立体效应共同作用的结果, 由于N―C键长比S―C键长短, NH基团取代导致烷基链的翻转, 同时, 磺酸基团限制了链的翻转, 因此改变了抑制剂的结合模式. 计算结果与实验基本一致.本文的研究结果有助于进一步理解含锍离子的葡萄糖苷酶抑制剂的结合机理, 并为设计更有潜力的葡萄糖苷酶抑制剂提供了有价值的信息.