Chun P W
Department of Biochemistry, University of Florida College of Medicine, Gainesville, Florida 32610-0245 USA.
Biophys J. 2000 Jan;78(1):416-29. doi: 10.1016/S0006-3495(00)76604-5.
It is well known that essentially all biological systems function over a very narrow temperature range. Most typical macromolecular interactions show DeltaH degrees (T) positive (unfavorable) and a positive DeltaS degrees (T) (favorable) at low temperature, because of a positive (DeltaCp degrees /T). Because DeltaG degrees (T) for biological systems shows a complicated behavior, wherein DeltaG degrees (T) changes from positive to negative, then reaches a negative value of maximum magnitude (favorable), and finally becomes positive as temperature increases, it is clear that a deeper-lying thermodynamic explanation is required. This communication demonstrates that the critical factor is a temperature-dependent DeltaCp degrees (T) (heat capacity change) of reaction that is positive at low temperature but switches to a negative value at a temperature well below the ambient range. Thus the thermodynamic molecular switch determines the behavior patterns of the Gibbs free energy change and hence a change in the equilibrium constant, K(eq), and/or spontaneity. The subsequent, mathematically predictable changes in DeltaH degrees (T), DeltaS degrees (T), DeltaW degrees (T), and DeltaG degrees (T) give rise to the classically observed behavior patterns in biological reactivity, as may be seen in ribonuclease S' fragment complementation reactions.
众所周知，基本上所有生物系统都在非常狭窄的温度范围内发挥作用。由于（ΔCp°/T）为正值，大多数典型的大分子相互作用在低温下显示出ΔH°（T）为正（不利）且ΔS°（T）为正（有利）。由于生物系统的ΔG°（T）表现出复杂的行为，即ΔG°（T）从正值变为负值，然后达到最大幅度的负值（有利），最后随着温度升高变为正值，显然需要更深入的热力学解释。本通讯表明，关键因素是反应的温度依赖性ΔCp°（T）（热容变化），其在低温下为正，但在远低于环境范围的温度下转变为负值。因此，热力学分子开关决定了吉布斯自由能变化的行为模式，进而决定了平衡常数K（eq）和/或自发性的变化。随后，ΔH°（T）、ΔS°（T）、ΔW°（T）和ΔG°（T）在数学上可预测的变化导致了生物反应中经典观察到的行为模式，如在核糖核酸酶S'片段互补反应中所见。
