Institute of New Energy Technology, Ningbo Institute of Materials Technology and Engineering , CAS , 1219 Zhongguan Road , 315201 Ningbo , P. R. China.
ACS Appl Mater Interfaces. 2018 Dec 5;10(48):41326-41337. doi: 10.1021/acsami.8b14125. Epub 2018 Nov 20.
Carbonic anhydrase (CA) was previously proposed as a green alternative for biomineralization of carbon dioxide (CO). However, enzyme's fragile nature when in synthetic environment significantly limits such industrial application. Herein, we hypothesized that CA immobilization onto flexible and hydrated "bridges" that ensure proton-transfer at their interfaces leads to improved activity and kinetic behavior and potentially increases enzyme's feasibility for industrial implementation. Our hypothesis was formulated considering that water plays a key role in the CO hydration process and acts as both the reactant as well as the rate-limiting step of the CO capture and transformation process. To demonstrate our hypothesis, two types of user-synthesized organic metallic frameworks [metal-organic frameworks (MOFs), one hydrophilic and one hydrophobic] were considered as model supports and their surface characteristics (i.e., charge, shape, curvature, size, etc.) and influence on the immobilized enzyme's behavior were evaluated. Morphology, crystallinity and particle size, and surface area of the model supports were determined by scanning electron microscopy, dynamic light scattering, and nitrogen adsorption/desorption measurements, respectively. Enzyme activity, kinetics, and stability at the supports interfaces were determined using spectroscopical analyses. Analysis showed that enzyme functionality is dependent on the support used in the immobilization process, with the enzyme immobilized onto the hydrophilic support retaining 72% activity of the free CA, when compared with that immobilized onto the hydrophobic one that only retained about 28% activity. Both CA-MOF conjugates showed good storage stability relative to the free enzyme in solution, with CA immobilized at the hydrophilic support also revealing increased thermal stability and retention of almost all original enzyme activity even after heating treatment at 70 °C. In contrast, free CA lost almost half of its original activity when subject to the same conditions. This present work suggests that MOFs tunable hydration conditions allow high enzyme activity and stability retention. Such results are expected to impact CO storage and transformation strategies based on CA and potentially increase user-integration of enzyme-based green technologies in mitigating global warming.
碳酸酐酶 (CA) 曾被提议作为生物矿化二氧化碳 (CO) 的绿色替代品。然而，酶在合成环境中的脆弱性质显著限制了这种工业应用。在此，我们假设 CA 固定在灵活且水合的“桥梁”上，这些桥梁在其界面处确保质子转移，从而导致活性和动力学行为得到改善，并可能增加酶在工业实施中的可行性。我们的假设是基于以下考虑：水在 CO 水合过程中起着关键作用，既是反应物，也是 CO 捕获和转化过程的限速步骤。为了验证我们的假设，我们考虑了两种类型的用户合成有机金属框架 [金属有机框架 (MOFs)，一种亲水，一种疏水] 作为模型支撑体，并评估了它们的表面特性（即电荷、形状、曲率、大小等）及其对固定化酶行为的影响。模型支撑体的形态、结晶度和粒径以及表面积分别通过扫描电子显微镜、动态光散射和氮气吸附/脱附测量来确定。通过光谱分析确定支撑体界面上的酶活性、动力学和稳定性。分析表明，酶的功能取决于固定化过程中使用的支撑体，与固定在疏水性支撑体上的酶相比，固定在亲水性支撑体上的酶保留了游离 CA 的 72%的活性，而固定在疏水性支撑体上的酶仅保留了约 28%的活性。与游离酶在溶液中的稳定性相比，两种 CA-MOF 缀合物都具有良好的储存稳定性，固定在亲水性支撑体上的 CA 还表现出更高的热稳定性和几乎所有原始酶活性的保留，即使在 70°C 的加热处理后也是如此。相比之下，游离 CA 在相同条件下几乎损失了一半的原始活性。本研究表明，MOFs 可调节水合条件，从而保持高酶活性和稳定性。这些结果有望影响基于 CA 的 CO 存储和转化策略，并可能增加酶基绿色技术在缓解全球变暖方面的用户整合。
