Cang-Rong Jason Teng, Pastorin Giorgia
Department of Pharmacy, National University of Singapore, Singapore.
Nanotechnology. 2009 Jun 24;20(25):255102. doi: 10.1088/0957-4484/20/25/255102. Epub 2009 Jun 2.
In the last decade, many environmental organizations have devoted their efforts to identifying renewable biosystems, which could provide sustainable fuels and thus enhance energy security. Amidst the myriad of possibilities, some biofuels make use of different types of waste biomasses, and enzymes are often employed to hydrolyze these biomasses and produce sugars that will be subsequently converted into ethanol. In this project, we aimed to bridge nanotechnology and biofuel production: here we report on the activity and structure of the enzyme amyloglucosidase (AMG), physically adsorbed or covalently immobilized onto single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs). In fact, carbon nanotubes (CNTs) present several properties that render them ideal support systems, without the diffusion limitations displayed by porous material and with the advantage of being further functionalizable at their surface. Chemical ligation was achieved both on oxidized nanotubes (via carbodiimide chemistry), as well as on amino-functionalized nanotubes (via periodate-oxidized AMG). Results showed that AMG retained a certain percentage of its specific activity for all enzyme-carbon nanotubes complexes prepared, with the physically adsorbed samples displaying better catalytic efficiency than the covalently immobilized samples. Analysis of the enzyme's structure through circular dichroism (CD) spectroscopy revealed significant structural changes in all samples, the degree of change being consistent with the activity profiles. This study proves that AMG interacts differently with carbon nanotubes depending on the method employed. Due to the higher activity reported by the enzyme physically adsorbed onto CNTs, these samples demonstrated a vast potential for further development. At the same time, the possibility of inducing magnetic properties into CNTs offers the opportunity to easily separate them from the original solution. Hence, substances to which they have been attached can be separated from a reaction medium, or directed by an external magnetic field to achieve efficient biofuel production. This paves the way for future design of efficient CNT-enzyme nanostructure bioreactors.
在过去十年中，许多环境组织致力于识别可再生生物系统，这些系统能够提供可持续燃料，从而增强能源安全。在众多可能性中，一些生物燃料利用不同类型的废弃生物质，并且通常使用酶来水解这些生物质并产生糖，随后这些糖将被转化为乙醇。在本项目中，我们旨在将纳米技术与生物燃料生产联系起来：在此我们报告了糖化酶（AMG）的活性和结构，该酶通过物理吸附或共价固定在单壁碳纳米管（SWNTs）和多壁碳纳米管（MWNTs）上。事实上，碳纳米管（CNTs）具有多种特性，使其成为理想的支撑体系，没有多孔材料所表现出的扩散限制，并且具有在其表面进一步功能化的优势。通过碳二亚胺化学在氧化的纳米管上以及通过高碘酸盐氧化的AMG在氨基功能化的纳米管上都实现了化学连接。结果表明，对于所有制备的酶 - 碳纳米管复合物，AMG都保留了一定比例的比活性，物理吸附的样品显示出比共价固定的样品更好的催化效率。通过圆二色性（CD）光谱对酶结构的分析揭示了所有样品中显著的结构变化，变化程度与活性谱一致。这项研究证明，根据所采用的方法，AMG与碳纳米管的相互作用方式不同。由于物理吸附在碳纳米管上的酶具有更高的活性，这些样品显示出巨大的进一步开发潜力。同时，将磁性引入碳纳米管的可能性提供了将它们与原始溶液轻松分离的机会。因此，与它们相连的物质可以从反应介质中分离出来，或者在外加磁场的引导下实现高效生物燃料生产。这为未来高效的碳纳米管 - 酶纳米结构生物反应器的设计铺平了道路。
