Isolation of the intra-crystalline proteins and kinetic studies in Struthio camelus (ostrich) eggshell for amino acid geochronology
Isolation of the intra-crystalline proteins and kinetic studies in Struthio camelus (ostrich) eggshell for amino acid geochronology
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DOI：
10.1016/j.quageo.2012.09.002
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发表时间：
2013-04-01
影响因子：
2.7
通讯作者：
Penkman, Kirsty
中科院分区：
文献类型：
--
作者：
Crisp, Molly;Demarchi, Beatrice;Penkman, Kirsty
鸵鸟蛋壳是氨基酸地质年代学的首选基质，产生了一致的结果，并被认为在蛋白质成岩作用方面接近于一个封闭系统。我们发现，鸵鸟蛋壳中的晶体内部分是更具挑战性的分离比从软体动物壳，需要72小时的氧化处理与次氯酸钠，导致损失高达一半的全壳蛋白。通过高温研究，我们已经表明，在连续浸出条件下，约99%的晶内氨基酸耐浸出。此外，在pH 5、7和9下的晶内蛋白质的高温实验表明，该级分不受该范围内pH变化的影响。本研究证实了OES中的晶体内蛋白质组分可能近似于一个封闭系统。晶体内的氨基酸已被证明遵循可预测的模式的水解和外消旋的所有氨基酸的研究。大多数氨基酸在有限的D/L范围内表现出一定的符合假可逆一级反应动力学的外消旋，但水解一般不好描述的一级动力学。因此，我们尝试了一种新的缩放方法来确定相对反应速率，通过应用缩放因子来重叠在不同温度下观察到的外消旋（或水解）速率来估计，其优点是不强制相对于时间的线性关系。使用表观一级动力学，约束的幂函数和缩放方法，我们估计的Arrhenius参数（活化能，EA和频率因子，A）的水解和外消旋。估算反应速率的不同方法可以给出明显不同但同样合理的活化能。这项研究加强了以前的工作，表明我们需要了解的基本机制，以估计准确的动力学参数。(C)2012爱思唯尔有限公司版权所有。
Ostrich eggshell is a favoured substrate for amino acid geochronology, yielding consistent results and thought to approximate a closed system with respect to protein diagenesis. We found that the intracrystalline fraction in ostrich eggshell is more challenging to isolate than that from mollusc shells, requiring 72 h oxidative treatment with NaOCl, resulting in a loss of up to half of the whole-shell protein. Through high temperature studies we have shown that under continuous leaching conditions approximately 99% of the intra-crystalline amino acids are resistant to leaching. Furthermore, high temperature experiments of the intra-crystalline proteins at pH 5, 7 and 9 have shown that this fraction is unaffected by pH changes over this range. This study confirms that the intra-crystalline protein fraction in OES may approximate a closed system. The intra-crystalline amino acids have been shown to follow predictable patterns of hydrolysis and racemization for all amino acids studied. Most amino acids showed some conformity to pseudo reversible first order reaction kinetics for racemization over limited D/L ranges, but hydrolysis was generally described poorly by first order kinetics. We therefore tried a new scaling method to determine relative reaction rates, estimated by applying scaling factors to overlap the observed rates of racemization (or hydrolysis) at the different temperatures, with the advantage of not forcing a linear relationship with respect to time. Using apparent first order kinetics, constrained power functions and scaling methods, we estimated the Arrhenius parameters (activation energy, EA and frequency factors, A) for both hydrolysis and racemization. The different methods for the estimation of reaction rates can give significantly different, but equally plausible, activation energies. This study reinforces previous work that indicates we need to understand the underlying mechanisms in order to estimate accurate kinetic parameters. (C) 2012 Elsevier B.V. All rights reserved.