Tiktopulo E I, Kajava A V
Institute of Protein Research, Russian Academy of Sciences, Moscow Region.
Biochemistry. 1998 Jun 2;37(22):8147-52. doi: 10.1021/bi980360n.
Thermal transitions of type I collagen fibrils were investigated by differential scanning calorimetry and spectrophotometry of turbidity within a wide range of external conditions. The advanced microcalorimeter allowed us to carry out the measurements at low concentrations of collagen (0.15-0.3 mg/mL). At these concentrations of collagen and under fibril-forming conditions, the melting curves display two pronounced heat adsorption peaks (at 40 and 55 degreesC). The low-temperature peak was assigned to the melting of monomeric collagen, while the high-temperature peak was assigned to the denaturation of collagen fibrils. It was shown that the denaturation of fibrils, in contrast to the monomeric collagen, is accompanied by a noticeable change in the partial specific heat capacity. Surprisingly, comparison of the collagen calorimetric curves in the fibril-forming and nonforming conditions revealed that DeltaCp of fibril denaturation is caused by a decrease in the Cp of collagen at premelting temperatures. This suggests the existence of an intermediate structural state of collagen in a transparent solution preceding fibril formation. Our study also shows that collagen fibrils formed prior to heating have thermodynamic parameters different from those of fibrils formed and denatured during heating in the calorimeter. Analysis of the data allowed us to determine the denaturation enthalpy of the mature fibrils and to conclude that the enthalpy plays a more important role in fibril stabilization than was previously assumed. The observed large DeltaCp value of fibril denaturation as well as the difference between thermodynamic parameters of the mature and newly formed fibrils is readily explained by the presence of water molecules in the fibril structure.
通过差示扫描量热法和在广泛外部条件下的浊度分光光度法研究了I型胶原纤维的热转变。先进的微量热计使我们能够在低浓度胶原蛋白（0.15 - 0.3 mg/mL）下进行测量。在这些胶原蛋白浓度和纤维形成条件下，熔化曲线显示出两个明显的热吸附峰（分别在40和55摄氏度）。低温峰归因于单体胶原蛋白的熔化，而高温峰归因于胶原纤维的变性。结果表明，与单体胶原蛋白不同，纤维的变性伴随着偏比热容的显著变化。令人惊讶的是，对纤维形成和非形成条件下的胶原蛋白量热曲线进行比较发现，纤维变性的ΔCp是由预熔温度下胶原蛋白的Cp降低引起的。这表明在纤维形成之前的透明溶液中存在胶原蛋白的中间结构状态。我们的研究还表明，加热前形成的胶原纤维具有与在量热计中加热过程中形成和变性的纤维不同的热力学参数。对数据的分析使我们能够确定成熟纤维的变性焓，并得出结论，焓在纤维稳定中起的作用比以前假设的更重要。观察到的纤维变性的大ΔCp值以及成熟纤维和新形成纤维的热力学参数之间的差异很容易通过纤维结构中水分子的存在来解释。
