Rani Andleeb, Zhao Yu, Yan Qiulin, Wang Ying, Ma Ran, Zhu Zhenyu, Wang Bo, Li Ting, Zhou Xiuwen, Hocart Charles H, Zhou Youping
Isotopomics in Chemical Biology (ICB), School of Chemistry and Chemical Engineering, Shaanxi University of Science and Technology, Xi'an 710021, China.
College of Science and Engineering, ARC Centre of Excellence for Australian Biodiversity and Heritage, Centre for Tropical Environmental and Sustainability Science, James Cook University, Cairns 4878, Australia.
Anal Chem. 2023 Mar 21;95(11):4871-4879. doi: 10.1021/acs.analchem.2c04384. Epub 2023 Mar 6.
The O/O ratio of α-cellulose in land plants has proved of interest for climate, environmental, physiological, and metabolic studies. Reliable application of such a ratio may be compromised by the presence of hemicellulose impurities in the α-cellulose product obtainable with current extraction methods, as the impurities are known to be isotopically different from that of the α-cellulose. We first compared the quality of hydrolysates of "α-cellulose products" obtained with four representative extraction methods (Jayme and Wise; Brendel; Zhou; Loader) and quantified the hemicellulose-derived non-glucose sugars in the α-cellulose products from 40 land grass species using gas chromatography-mass spectrometry (GC/MS). Second, we performed compound-specific isotope analysis of the hydrolysates using GC/Pyrolysis/IRMS. These results were then compared with the bulk isotope analysis using EA/Pyrolysis/IRMS of the α-cellulose products. We found that overall, the Zhou method afforded the highest purity α-cellulose as judged by the minimal presence of lignin and the second-lowest presence of non-glucose sugars. Isotopic analysis then showed that the O-2-O-6 of the α-cellulose glucosyl units were all depleted in O by 0.0-4.3 mUr (average, 1.9 mUr) in a species-dependent manner relative to the α-cellulose products. The positive isotopic bias of using the α-cellulose product instead of the glucosyl units stems mainly from the fact that the pentoses that dominate hemicellulose contamination in the α-cellulose product are relatively enriched in O (compared to hexoses) as they inherit only the relatively O-enriched O-2-O-5 moiety of sucrose, the common precursor of pentoses and hexoses in cellulose, and are further enriched in O by the (incomplete) hydrolysis.
陆地植物中α-纤维素的O/O比已被证明在气候、环境、生理和代谢研究中具有重要意义。由于目前提取方法获得的α-纤维素产品中存在半纤维素杂质，可能会影响该比率的可靠应用，因为已知这些杂质在同位素上与α-纤维素不同。我们首先比较了用四种代表性提取方法（Jayme和Wise；Brendel；Zhou；Loader）获得的“α-纤维素产品”水解产物的质量，并使用气相色谱-质谱联用仪（GC/MS）对40种陆地草类物种的α-纤维素产品中半纤维素衍生的非葡萄糖糖进行了定量分析。其次，我们使用GC/热解/同位素比质谱仪（GC/Pyrolysis/IRMS）对水解产物进行了化合物特异性同位素分析。然后将这些结果与使用元素分析仪/热解/同位素比质谱仪（EA/Pyrolysis/IRMS）对α-纤维素产品进行的整体同位素分析进行比较。我们发现，总体而言，以木质素含量最低和非葡萄糖糖含量第二低来判断，Zhou方法得到的α-纤维素纯度最高。同位素分析表明，相对于α-纤维素产品，α-纤维素葡萄糖基单元的O-2-O-6在O中均以物种依赖的方式贫化了0.0-4.3‰（平均为1.9‰）。使用α-纤维素产品而非葡萄糖基单元产生的正同位素偏差主要源于这样一个事实，即α-纤维素产品中占主导的半纤维素污染物戊糖在O中相对富集（与己糖相比），因为它们仅继承了纤维素中戊糖和己糖的共同前体蔗糖中相对富含O的O-2-O-5部分，并且通过（不完全）水解进一步在O中富集。
