Novozymes, Inc., 1445 Drew Avenue, Davis, CA 95618, USA.
Appl Environ Microbiol. 2010 Dec;76(23):7673-82. doi: 10.1128/AEM.01376-10. Epub 2010 Oct 1.
Enzymatic lignocellulose hydrolysis plays a key role in microbially driven carbon cycling and energy conversion and holds promise for bio-based energy and chemical industries. Cellulases (key lignocellulose-active enzymes) are prone to interference from various noncellulosic substances (e.g., metal ions). During natural cellulolysis, these substances may arise from other microbial activities or abiotic events, and during industrial cellulolysis, they may be derived from biomass feedstocks or upstream treatments. Knowledge about cellulolysis-inhibiting reactions is of importance for the microbiology of natural biomass degradation and the development of biomass conversion technology. Different metal ions, including those native to microbial activity or employed for biomass pretreatments, are often tested for enzymatic cellulolysis. Only a few metal ions act as inhibitors of cellulases, which include ferrous and ferric ions as well as cupric ion. In this study, we showed inhibition by ferrous/ferric ions as part of a more general effect from oxidative (or redox-active) metal ions and their complexes. The correlation between inhibition and oxidation potential indicated the oxidative nature of the inhibition, and the dependence on air established the catalytic role that iron ions played in mediating the dioxygen inhibition of cellulolysis. Individual cellulases showed different susceptibilities to inhibition. It is likely that the inhibition exerted its effect more on cellulose than on cellulase. Strong iron ion chelators and polyethylene glycols could mitigate the inhibition. Potential microbiological and industrial implications of the observed effect of redox-active metal ions on enzymatic cellulolysis, as well as the prevention and mitigation of this effect in industrial biomass conversion, are discussed.
酶促木质纤维素水解在微生物驱动的碳循环和能量转化中起着关键作用，有望应用于生物基能源和化学工业。纤维素酶（关键的木质纤维素活性酶）容易受到各种非纤维素物质（例如金属离子）的干扰。在自然纤维素水解过程中，这些物质可能来自其他微生物活动或非生物事件，而在工业纤维素水解过程中，它们可能来自生物质原料或上游处理。了解纤维素抑制反应对于自然生物质降解的微生物学和生物质转化技术的发展都很重要。不同的金属离子，包括微生物活动中固有的或用于生物质预处理的金属离子，经常被用于测试酶促纤维素水解。只有少数几种金属离子作为纤维素酶的抑制剂，包括亚铁和铁离子以及铜离子。在这项研究中，我们展示了亚铁/铁离子的抑制作用，这是氧化（或氧化还原活性）金属离子及其配合物的更普遍作用的一部分。抑制作用与氧化还原电势之间的相关性表明了抑制作用的氧化性质，而对空气的依赖性则确立了铁离子在介导氧对纤维素水解抑制作用中的催化作用。个别纤维素酶对抑制作用的敏感性不同。这种抑制作用可能更针对纤维素而不是纤维素酶。强的铁离子螯合剂和聚乙二醇可以减轻抑制作用。讨论了氧化还原活性金属离子对酶促纤维素水解的影响以及在工业生物质转化中预防和减轻这种影响的潜在微生物学和工业意义。
