牛胰RNaseA的热转变的差示扫描量热研究

A DSC STUDY ON THE THERMOTRANSITIONS OF BOVINE PANCREATIC RIBONUCLEADE A

用差示扫描量热法对含水量为0.05-3.15克/克的牛胰核糖核酸酶A的热转变进行了研究.当R<0.40克/克时,在315-345和400-450K左右,分别观察到峰Ⅰ和峰Ⅲ.文中对峰Ⅰ的“恢复”进行了讨论.在R<1.1克/克时,通常被认为热变性峰的峰Ⅱ的峰温,随R的增加而降低,变性热随R的增加而减少,但在 R≥1.1克/克时,二者均取稳定值,Ttr=335.5K和Qtr=7.38CaⅠ/go峰Ⅱ的半宽在R=0.40克/克处取极小值,在R≥1.65时取稳定值,△T1/2=7.34K,文中首次给出了水合状态下热变性峰的转变热和峰温的关系曲水线.对水合球状蛋白的热变性的一种可能解释为,变性焓是温度的函数,而转变温度直接受含水量影响.

The thermotransitions of bovine pancreatic ribonuclease A with water content (R) from 0.05 to 3.15 g(H2O)/g(protein) were studied by differential scanning calorimetry. When R<0.40 g/g, peak I and peak I were observed in the temperature range from 315 to 345 and from 400 to about 459 K, respectively. The 'reappearance' of peak I has been discussed. When R<1.1g/g, the tempe-rature of peak II, known as the denaturational peak, decreases with R and the heat of the peak increases with R. But they all remain steady in the region R≥1.1 g/g, Ttz= 335.5 K and Qtz = 7.38 cal/g(protein). The half width of peak II has its minimum value at R = 0.40 g/g and reaches its steady value at about R=1.65 g/g. A new plot, transitional heat vs temperature, for peak II of the protein has been provided, which gives rise to a possible interpertation of the denatu denaturation of hydrated proteins: the enthalpy of the denatura-tion of a protein is a direct function of the denataration temperature which depends upon the hydration of the protein.