Effect of D2O on the Thermal Stability of the β Conformation of Poly[S-((3-hydroxypropyl) carbamoylmethyl)-L-cysteine]
Effect of D2O on the Thermal Stability of the β Conformation of Poly[S-((3-hydroxypropyl) carbamoylmethyl)-L-cysteine]
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D2O对聚[S-((3-羟丙基)氨基甲酰甲基)-L-半胱氨酸]β构象热稳定性的影响
DOI：
10.1021/ma60067a039
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发表时间：
1979
期刊：
影响因子：
--
通讯作者：
S. Ikeda
中科院分区：
文献类型：
--
作者：
T. Tomiyama;S. Ikeda
已知聚（S-（羧甲基）-L-半胱氨酸）在水溶液中会发生pH诱导的/3-螺旋转变，1，2，我们最近发表了一篇关于其圆二色性和/3-螺旋转变的论文。3.为了避免离子化基团的静电效应带来的复杂性，我们制备了一种水溶性的、不可离子化的多肽聚[S-（（3-羟丙基）氨甲酰甲基）-L-半胱氨酸]（poly [Cys（CamPrOH）]），并通过圆二色谱研究了它在水溶液中的构象。本文报道了聚[Cys（CamPrOH）]在D_（20）中的构象随温度变化的特征。4聚（S-（苄氧羰基甲基）-L-半胱氨酸）5在60 ℃下用大量过量的3-氨基丙醇酰胺化几天，并将反应混合物倒入3%乙酸溶液中。将溶液用蒸馏水透析后，通过冻干分离聚[Cys（CamPrOH）]。聚[Cys（CamPrOH）]可溶于二氯乙酸（DCA），但微溶于水。样品代码，TX-4071：0.1% CH 3COOH溶液中Mn 12 000，[] 25 ℃下DCA中0.31 dL g-1。由水溶液浇铸的固体膜的红外光谱显示在1625 cm-1处的酰胺I带和在1528 cm-1处的酰胺II带。然后聚[Cys（CamPrOH）]在固态下处于双链结构。图1显示了聚[Cys-（CamPrOH）]在25 ℃的H2O中和在不同温度的D2 O中的圆二色性，其浓度为约0.02g dL-1或10 - 3 N。H2O溶液的圆二色性不随温度而明显改变;其在198和225 nm附近具有两个负带。该光谱与完全电离状态下的聚（S-（羧甲基）-L-半胱氨酸）的光谱相似，3因此，聚-[Cys（CamPrOH）]在H2O中的构象归属于无规卷曲。另一方面，D20溶液的圆二色性强烈依赖于温度。在1.5 ℃下，光谱在198 nm处有一个强的正带，在227 nm处有一个负带，与低电离度下的聚（S-（羧甲基）-L-半胱氨酸）相似。3.在低温下，在D20溶液中，聚半胱氨酸（CamPrOH）]呈双链构象。随着温度的升高，圆二色性发生明显变化，正负谱带都变得
Poly (S-(carboxymethyl)-L-cysteine) is known to undergo a pH-induced/3-coil transition in aqueous solution, 1, 2 and we have recently published a paper concerning its circular dichroism and/3-coil transition in detail. 3 In order to avoid the complication arising from the electrostatic effect of ionized groups, we have prepared a water-soluble, non-ionizable polypeptide, poly [S-((3-hydroxypropyl) carba-moylmethyl)-L-cysteine](poly [Cys (CamPrOH)], and investigated its conformation in aqueous solutions by measurement of circular dichroism. In this communication we report the characteristic temperature dependence of its conformation in D20.Poly [Cys (CamPrOH)] was synthesized by a method similar to that for preparingpoly [JV5-(3-hydroxypropyl)-L-glutamine]. 4 Poly (S-(carbobenzoxymethyl)-L-cys-teine) 5 was amidated by a large excess of 3-aminopropanol at 60 C for a few days, and the reaction mixture was poured into a 3% acetic acid solution. After the solution was dialyzed against distilled water, poly [Cys (CamPrOH)] was isolated by lyophilization. Poly [Cys (CamPrOH)] is soluble in dichloroacetic acid (DCA) but is sparingly soluble in water. Sample code, TX-4071: Mn 12 000 in 0.1% CH3COOH solution,[] 0.31 dL g'1 in DCA at 25 C. The infrared spectra of solid film cast from an aqueous solution shows an amide I band at 1625 cm'1 and an amide II band at 1528 cm'1. Then poly [Cys (CamPrOH)] is in the ß structure in the solid state. Figure 1 shows the circular dichroism of poly [Cys-(CamPrOH)] in H20 at 25 C and in D20 at different temperatures, the concentrations of which are about 0.02 g dL'1 or 10" 3 N. Circular dichroism of an H20 solution does not change appreciably with temperature; it has two negative bands around 198 and 225 nm. This spectrum is similar to that ofpoly (S-(carboxymethyl)-L-cysteine) in the fully ionized state, 3 andthe conformation of poly-[Cys (CamPrOH)] in H20 is, therefore, assigned to the random coil. On the other hand, circular dichroism of a D20 solution is strongly dependent on temperature. At 1.5 C the spectrum has a strong positive band at 198 nm and a negative band at 227 nm and is similar to that of poly (S-(carboxymethyl)-L-cysteine) at low degrees of ionization. 3 Then polyfCys (CamPrOH)] is in the ß con-formation in D20 solution at low temperature. With increasing temperature, the circular dichroism changes markedly, both positive and negative bands becoming