Biosystem and Agricultural Engineering Department, University of Kentucky, 115 C.E. Barnhart Building, Lexington, KY 40546, USA.
Enzyme Microb Technol. 2013 Apr 10;52(4-5):258-64. doi: 10.1016/j.enzmictec.2013.01.008. Epub 2013 Jan 31.
The work investigated the properties and feasibility of using bacterial cellulose membrane (BCM) as a new and environmental friendly support carrier to immobilize glutamate decarboxylase (GAD) (a unique enzyme in the conversion of γ-aminobutyric acid (GABA) production). During cultivation, the porosities of BCM decreased successively with more extended fibrils piling above one another in a criss-crossing manner thus forming condensed and spatial structure. The BCM with this ultrafine network structure was found to immobilize GAD best via covalent binding because of the highest efficiency of immobilization (87.56% of the enzyme was bonded) and a good operational stability. And the covalent binding efficiency (amount of enzyme immobilized versus lost) was closely related to the porosity or the inner network of the BCM, not to the surface area. The capacity per surface area (mg/cm(2)) increased from 1.267mg/cm(2) to 3.683mg/cm(2) when the porosity of BCM ranged from 49% to 73.80%, while a declining trend of the loss of GAD specific activity (from 29.30%/cm(2) to 7.38%/cm(2)) was observed when the porosity increased from 49.9% to 72.30%. Two non-linear regression relationships, between the porosity and loading capacity and between porosity and enzyme activity loss, were empirically modeled with the determination of coefficient R(2) of 0.980 and 0.977, respectively. Finally, the established in vitro enzymatic conversion process demonstrated 6.03g/L of GABA at 0.10mol/L Glu, 60min of retention time and 160mL of suspension volume after the 1st run and a loss of 4.15% after the 4th run. The productivity of GABA was 6.03gL(-1)h(-1), higher than that from other reported processes.
该工作研究了细菌纤维素膜（BCM）作为一种新型环保支撑载体固定谷氨酸脱羧酶（GAD）（一种独特的酶，用于γ-氨基丁酸（GABA）生产的转化）的特性和可行性。在培养过程中，BCM 的孔隙率逐渐降低，更多的纤维彼此交叉堆积，形成密集的空间结构。具有这种超细网络结构的 BCM 被发现通过共价键固定 GAD 的效果最佳，因为固定化效率最高（结合了 87.56%的酶），并且具有良好的操作稳定性。并且共价键合效率（固定的酶量与损失的酶量之比）与 BCM 的孔隙率或内部网络密切相关，而与表面积无关。当 BCM 的孔隙率从 49%增加到 73.80%时，比表面积的容量（mg/cm(2)）从 1.267mg/cm(2)增加到 3.683mg/cm(2)，而当 BCM 的孔隙率从 49.9%增加到 72.30%时，GAD 比活性的损失呈下降趋势（从 29.30%/cm(2)到 7.38%/cm(2)）。用决定系数 R(2)分别为 0.980 和 0.977 对孔隙率与装载量之间以及孔隙率与酶活性损失之间的两个非线性回归关系进行了经验建模。最后，建立的体外酶转化过程在 1 次运行后，Glu 为 0.10mol/L、保留时间为 60min、悬浮液体积为 160mL 时，得到 6.03g/L 的 GABA，在第 4 次运行后损失 4.15%。GABA 的生产力为 6.03gL(-1)h(-1)，高于其他报道的过程。
