Department of Biochemistry, University of Wisconsin-Madison , Madison, Wisconsin 53706, United States.
Department of Energy, Great Lakes Bioenergy Research Center, Wisconsin Energy Institute , Madison, Wisconsin 53726, United States.
Biomacromolecules. 2017 Dec 11;18(12):4184-4195. doi: 10.1021/acs.biomac.7b01223. Epub 2017 Nov 8.
Protein polymers exist in every plant cell wall preparation, and they interfere with lignin characterization and quantification. Here, we report the structural characterization of the residual protein peaks in 2D NMR spectra in corn cob and kenaf samples and note that aromatic amino acids are ubiquitous and evident in spectra from various other plants and tissues. The aromatic correlations from amino acid residues were identified and assigned as phenylalanine and tyrosine. Phenylalanine's 3/5 correlation peak is superimposed on the peak from typical lignin p-hydroxyphenyl (H-unit) structures, causing an overestimation of the H units. Protein contamination also occurs when using cellulases to prepare enzyme lignins from virtually protein-free wood samples. We used a protease to remove the protein residues from the ball-milled cell walls, and we were able to reveal H-unit structures in lignins more clearly in the 2D NMR spectra, providing a better basis for their estimation.
蛋白质聚合物存在于每个植物细胞壁准备中，并干扰木质素的特征和定量。在这里，我们报告了玉米芯和麻疯树样品二维 NMR 光谱中残留蛋白质峰的结构特征，并注意到芳香族氨基酸在各种其他植物和组织的光谱中普遍存在且明显。鉴定并分配了氨基酸残基的芳族相关物，为苯丙氨酸和酪氨酸。苯丙氨酸的 3/5 相关峰与典型木质素对羟基苯基（H 单元）结构的峰叠加，导致 H 单元的高估。当使用纤维素酶从实际上不含蛋白质的木材样品制备酶木质素时，也会发生蛋白质污染。我们使用蛋白酶从球磨细胞壁中去除蛋白质残基，并且我们能够在二维 NMR 光谱中更清楚地揭示木质素中的 H 单元结构，为其估算提供了更好的基础。
