PDF(Pubmed)
Abstract：
Understanding the nitrogen isotopic variations of individual amino acids (AAs) is essential for utilizing the nitrogen isotope values of individual amino acids (δ15N-AA) as source indicators to identify proteinaceous matter originating from biomass combustion processes. However, the nitrogen isotope effects (ε) associated with the degradation of individual amino acids during combustion processes have not been previously explored. In this study, we measured the nitrogen isotope values of residual free amino acids -following a series of controlled combustion experiments at temperatures of 160-240 °C and durations of 2 min to 8 h, as described in Part 1. δ15N values of proline, aspartate, alanine, valine, glycine, leucine, and isoleucine are more positive than their initial δ15N values after prolonged combustion. Variations in δ15N values of the most AAs conform to the Rayleigh fractionation during combustion and their nitrogen isotope effects (ε) are greatly impacted by their respective combustion degradation pathways. This is the first time the ε values associated with the degradation pathways of AAs during combustion have been characterized. Only the ε values associated with Pathway 1 (dehydration to form dipeptide) and 2 (simultaneous deamination and decarboxylation) are found to be significant and temperature-dependent, ranging from + 2.9 to 6.4‰ and + 0.9‰ to + 3.8‰, respectively. Conversely, ε values associated with other pathways are minor. This improves the current understanding on the degradation mechanisms of protein nitrogen during biomass burning.
摘要：
了解单个氨基酸（AA）的氮同位素变化对于利用单个氨基酸的氮同位素值（δ15N-AA）作为源指标来识别源自生物质燃烧过程的蛋白质物质至关重要。然而,先前尚未研究过与燃烧过程中单个氨基酸降解相关的氮同位素效应（ε）。在这项研究中,我们测量了残留游离氨基酸的氮同位素值-在160-240°C的温度和2分钟至8小时的持续时间下进行了一系列受控燃烧实验，如第1部分所述。脯氨酸的δ15N值，天冬氨酸,丙氨酸,缬氨酸,甘氨酸,亮氨酸,和异亮氨酸在长时间燃烧后比它们的初始δ15N值正。大多数AA的δ15N值的变化符合燃烧过程中的瑞利分馏，它们的氮同位素效应（ε）受到各自燃烧降解途径的极大影响。这是首次表征与燃烧过程中AA的降解途径相关的ε值。只有与途径1（脱水形成二肽）和途径2（同时脱氨和脱羧）相关的ε值被发现是显著的和温度依赖性的，范围从+2.9到6.4‰,+0.9到+3.8‰,分别。相反，与其他途径相关的ε值是次要的。这改善了目前对生物质燃烧过程中蛋白质氮降解机理的理解。
