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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Spectroscopy of Hydrothermal Reactions 25: Kinetics of the Decarboxylation of Protein Amino Acids and the Effect of Side Chains on Hydrothermal Stability
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Spectroscopy of Hydrothermal Reactions 25: Kinetics of the Decarboxylation of Protein Amino Acids and the Effect of Side Chains on Hydrothermal Stability

机译：水热反应的光谱学25：蛋白质氨基酸脱羧的动力学和侧链对水热稳定性的影响

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摘要

The stability toward decarboxylation of six protein amino acids with functionally substituted side chains [phenylalanine (Phe), serine (Ser), threonine (Thr), proline (Pro), histidine (His), and methionine (Met)] were studied with an FT-IR spectroscopy flow reactor at pH_(25) 1.5-8.5, T = 270-340 ℃, and P = 275 bar. The first-order (or pseudo-first-order) rate constants and Arrhenius parameters were obtained on the basis of the rate of CO_2 formation. The decarboxylation rates of Phe, Ser, Thr, Pro, and Met are independent of pH in the range of 3-8.5. At pH 1.5-3, a maximum rate constant occurs at about 2.5. His has a different pH-rate profile. At its natural pH_(25) (7.44), the decarboxylation rate reaches a minimum, but increasing or decreasing the pH increases the rate. The activation energies and preexponential factors for the decarboxylation of the protein amino acids cover a wide range. However, a strong correlation between E_a and ln(A) (the kinetic compensation effect) exists, which implies that the amino acids share the same mechanism or at least the same rate-determining step regardless of the side chain. Combining the observations about decarboxylation, deamination, and dehydration, we discuss the effects of the side chains on the hydrothermal stability of protein amino acids in terms of their structures.
机译：研究了用功能取代的侧链[苯丙氨酸（Phe），丝氨酸（Ser），苏氨酸（Thr），脯氨酸（Pro），组氨酸（His）和蛋氨酸（Met）]对六个蛋白质氨基酸的脱羧稳定性。 FT-IR光谱流动反应器，pH_（25）1.5-8.5，T = 270-340℃，P = 275 bar。一阶（或伪一阶）速率常数和Arrhenius参数是基于CO_2生成速率获得的。 Phe，Ser，Thr，Pro和Met的脱羧速率与pH值无关，在3-8.5范围内。在pH 1.5-3时，最大速率常数约为2.5。他的pH速率曲线不同。在其自然pH_（25）（7.44）下，脱羧速率达到最小值，但是增加或降低pH会使脱羧速率增加。蛋白质氨基酸脱羧的活化能和指数因子覆盖范围很广。但是，E_a和ln（A）之间存在很强的相关性（动力学补偿效应），这意味着氨基酸具有相同的机制或至少具有相同的速率确定步骤，而与侧链无关。结合对脱羧，脱氨基和脱水的观察，我们讨论了侧链对蛋白质氨基酸的水热稳定性的影响。

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