If y>x and these two reactions are coupled (generally through a complex reaction path on an enzyme), then we have:Īlthough one can reject the second explanation in the question as it stands because it ignores the free energy change in the protein folding, perhaps it was intended to mean that the folding of the protein (A → B) should be considered as coupled to the change in the environment of the water (C → D), and that the negative ΔG for the aqueous environment made a greater contribution to the overall ΔG than that for the protein folding. Many biochemical changes involve transformations which individually have a positive free energy change, but are made possible by coupling to another reaction with negative free energy change, of greater magnitude:
This approach has been applied to the structural change of protein folding with the conclusion (consistent with the first explanation) that the change in enthalpy (ΔH) is sufficient to produce a negative ΔG and hence drive protein folding (Citation 1, below).įree energy change in coupled transformations have a negative enthalpy change (ΔH) ) which affects its aqueous surroundings, but it seems justified to consider the reaction in isolation as there is no sense that the change in the vibration of the water molecules is driving or coupled to the reaction. A chemical reaction for which ΔG is negative may generate heat (i.e. It is standard practice in biochemistry to consider the Gibbs Free Energy of transformation of the sort A → B in isolation in determining whether it will proceed spontaneously. This view has been persuasively advocated on the basis of experimental measurements.įree energy change in individual transformations The assertion would then be that a negative free-energy change in the water system is the deciding factor. A modification of the second explanation (perhaps what was intended) is that it is necessary to consider the protein folding and change in the water as being coupled, in which case the overall free energy change - the sum of the two considered separately - is the determinant of protein folding.
The second explanation cannot be correct, as it stands, as it ignores the free energy change in the protein.The first explanation is commonly encountered.
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