Rudolph A S, Crowe J H
Biophys J. 1986 Sep;50(3):423-30. doi: 10.1016/S0006-3495(86)83478-6.
We have studied the calorimetric and infrared spectroscopic properties of the amino acid proline which has been implicated in the stabilization of biomacromolecules during reduced water states. It has been suggested that the ability of this molecule to protect biomacromolecules during these stress states may be related to the formation of polymeric aggregates of proline monomers in solution. The structure of this aggregate is thought to be an alternates stack, forming a hydrophilic colloid-like polymer which is thought to interact with hydrophobic moieties of biomacromolecules, reducing the exposed hydrophobic area during reduced water conditions. Calorimetric data presented in this work show that in increasing concentration of proline in solution the enthalpy associated with the melting of bulk water is greatly reduced, indicating strong hydrogen bonding character of proline in aqueous solution. Proline shows two eutectic phase separations at moderate concentrations and one of these eutectics may be the proposed intermolecular state. A partial phase diagram for proline is presented. Fourier-transform infrared spectroscopic data indicate that the COO- asymmetric stretch of proline shows marked splitting with increasing proline concentration. This suggests that the carboxylate is in different environments, with the high energy vibrations representing COO- groups which are participating in the hydrogen bonding pattern associated with the formation of the intermolecular stack. Changes in the CH2 asymmetric and symmetric stretches of the pyrrolidine rings of proline are consistent with the proposed stack structure. We also suggest a possible mechanism by which these intermolecular associations may be important in the protection of biomacromolecules during reduced water states.
我们研究了氨基酸脯氨酸的量热和红外光谱性质，脯氨酸在水分减少状态下对生物大分子的稳定作用中发挥作用。有人提出，该分子在这些应激状态下保护生物大分子的能力可能与脯氨酸单体在溶液中形成聚合物聚集体有关。这种聚集体的结构被认为是交替堆叠，形成一种亲水性胶体状聚合物，该聚合物被认为与生物大分子的疏水部分相互作用，在水分减少的条件下减少暴露的疏水区域。这项工作中给出的量热数据表明，随着溶液中脯氨酸浓度的增加，与大量水熔化相关的焓大幅降低，这表明脯氨酸在水溶液中具有很强的氢键特性。脯氨酸在中等浓度下表现出两个共晶相分离，其中一个共晶可能是所提出的分子间状态。给出了脯氨酸的部分相图。傅里叶变换红外光谱数据表明，脯氨酸的COO-不对称伸缩随着脯氨酸浓度的增加显示出明显的分裂。这表明羧酸盐处于不同的环境中，高能量振动代表参与与分子间堆叠形成相关的氢键模式的COO-基团。脯氨酸吡咯烷环的CH2不对称和对称伸缩的变化与所提出的堆叠结构一致。我们还提出了一种可能的机制，通过该机制这些分子间缔合在水分减少状态下对生物大分子的保护中可能很重要。
