The triple helix ⇌ coil conversion of collagen‐like polytripeptides in aqueous and nonaqueous solvents. Comparison of the thermodynamic parameters and the binding of water to (L‐Pro‐L‐Pro‐Gly)n and (L‐Pro‐L‐Hyp‐Gly)n
The triple helix ⇌ coil conversion of collagen‐like polytripeptides in aqueous and nonaqueous solvents. Comparison of the thermodynamic parameters and the binding of water to (L‐Pro‐L‐Pro‐Gly)n and (L‐Pro‐L‐Hyp‐Gly)n
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类胶原蛋白多肽在水性和非水性溶剂中的三螺旋⇌卷曲转化的热力学参数以及水与 (L-Pro-L-Pro-Gly)n 和 (L-Pro-L-Hyp- 的结合的比较。甘氨酸)n
DOI：
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发表时间：
1977
期刊：
影响因子：
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通讯作者：
H. Klump
中科院分区：
文献类型：
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作者：
J. Engel;Han Chen;D. Prockop;H. Klump
检查胶原样肽（L-Pro-L-Pro-Gly）n和（L-Pro-L-Hyp-Gly）n（n = 5和10）在水性和非水性溶剂中的三螺旋双螺旋转变。这些肽可溶于含有3%乙酸的1，2-丙二醇中，并且发现它们在该溶剂体系中形成三螺旋结构。通过用分子筛平衡溶剂并对溶剂相进行Karl Fischer滴定来测定溶剂体系的水含量和与肽结合的水量。在溶剂脱水后，每个三肽单元与肽结合的水分子远少于一个。由于肽保持三螺旋构象，结果表明水不是三螺旋结构的必要组分。具有相同链长的肽的比较表明，即使在无水条件下，羟脯氨酸的存在也增加了三螺旋的热稳定性。因此，结果不支持最近的假设，即羟脯氨酸通过与水分子的特异性相互作用稳定胶原蛋白和胶原蛋白样肽的三螺旋。对几种溶剂体系中热转变曲线的分析表明，尽管含羟脯氨酸的肽的tm值高18.6° ~ 32.7°C，但在25°C时，羟脯氨酸对ΔG的影响仅为0.1 ~ 0.3 kcal/三肽单位。结果表明，因此，羟基脯氨酸对螺旋稳定性的影响可以解释为固有的影响，如偶极-偶极相互作用或由醇，乙酸和水的肽的溶剂化的变化。在3%或10%乙酸中对（L-Pro-L-Pro-Gly）n的转变焓进行直接量热测量，得到卷曲至螺旋转变的值为每三肽单位−1.84 kcal。根据焓值和不同链长对热转变影响的数据，计算出25°C时成核的表观自由能为+5 kcal/mol（表观成核参数= 2 × 10−4 M−2）。该值取决于溶剂和末端基团的化学修饰。
The collagen‐like peptides (L‐Pro‐L‐Pro‐Gly)n and (L‐Pro‐L‐Hyp‐Gly)n with n = 5 and 10, were examined in terms of their triple helix ⇌ coil transitions in aqueous and nonaqueous solvents. The peptides were soluble in 1,2‐propanediol containing 3% acetic acid and they were found to form triple‐helical structures in this solvent system. The water content of the solvent system and the amount of water bound to the peptides were assayed by equilibrating the solvent with molecular sieves and carrying out Karl Fischer titrations on the solvent phase. After the solvent was dehydrated, much less than one molecule of water per tripeptide unit was bound to the peptides. Since the peptides remained in a triple‐helical conformation, the results indicated that water was not an essential component of the triple‐helical structure. Comparison of peptides with the same chain length demonstrated that the presence of hydroxyproline increased the thermal stability of the triple helix even under anhydrous conditions. The results, therefore, did not support recent hypotheses that hydroxyproline stabilizes the triple helix of collagen and collagen‐like peptides by a specific interaction with water molecules. Analysis of the thermal transition curves in several solvent systems showed that although the peptides containing hydroxyproline had tm values which were 18.6° to 32.7°C higher, the effect of hydroxyproline on ΔG was only 0.1 to 0.3 kcal per tripeptide unit at 25°C. The results suggested, therefore, that the influence of hydroxyproline on helical stability may be explained by intrinsic effects such as dipole–dipole interactions or by changes in the solvation of the peptides by alcohol, acetic acid, and water. A direct calorimetric measurement of the transition enthalpy for (L‐Pro‐L‐Pro‐Gly)n in 3% or 10% acetic acid gave a value of −1.84 kcal per tripeptide unit for the coil‐to‐helix transition. From the value for enthalpy and from data on the effects of different chain lengths on the thermal transition, it was calculated that the apparent free energy for nucleation was +5 kcal/mol at 25°C (apparent nucleation parameter = 2 × 10−4 M−2). The value was dependent on solvent and on chemical modification of end groups.