【摘要】 应用微热量计研究了棕色固氮菌固氮酶铁蛋白与MgATP或MgADP络合的热力学状况。在25℃,1大气压下铁蛋白与MgATP饱和络合时的焓(⊿H~0)变化为-4.78千卡/摩尔,自由能(AGO)变化为-6.66千卡/摩尔,熵(⊿S~0)变化为+6.31卡·度/摩尔。在铁蛋白与MgATP络合时,随着MgATP浓度的增加,-⊿H~0也随之增加呈S型曲线,铁蛋白与MgADP饱和络合时⊿H~0为-5.45千卡/摩尔,AGO为-6.89千卡/摩尔,⊿S~0为+4.82卡·度/摩尔。熵的增加表明MgATP或MgADP与铁蛋白络合后,引起铁蛋白构型的变化。铁蛋白与MgATP或MgADP饱和络合时的TASO分别为+1.88千卡/摩尔和+1.44千卡/摩尔。更多还原

【Abstract】 The binding of MgATP and MgADP to iron protein of nitrogenase from Azotobacter vinelandii (Av2) has been studied by batch microcalorimeter and a ⊿H~0 value of -4.78 K cal/mole for ATP and -5.45 K cal/mole for ADP were measured. Such small enthalpy values combined with a ⊿G~0O value of -6.66 K cal/mole obtained for MgATP and -6.89 K cal/mole for MgADP binding to Av2 give ⊿S~0 values of +6.31 and +4.82 entropy units respectively. These data suggest that the binding energy resulting from the interaction of MgATP and MgADP with Av2 is conversed in the entropy change as T⊿S~0 energy amounting to +1.88 and + 1.44 K cal/mole respectively. The positive sign of the entropy change indicates a loosening of the Av2 structure and possibly the storage of some energy.更多还原