| Comments |
p.412 2nd paragraph: "From the change in equilibrium constant with temperature, ΔH for the binding reaction is + 8.5 kcal/mole. At 24°C the equilibrium association constant is 1×10^13/M, therefore, ΔF for the reaction is - 18 kcal/mole. The entropy change, ΔS, is thus + 90 cal/mole/deg, and is clearly the main driving force for the reaction. This change in entropy could arise from a change in configuration of repressor and/or operator. But, as is more likely, it could result from changes in the solvation of the reacting species." P.415 bottom paragraph: "The effect of temperature on kb/ka is such that the binding is less tight at 1 than at 24°C by about a factor of four, again the change being confined to the rate of association. This result confirms [investigators’] earlier equilibrium studies (Riggs et al., 1970b). In [their] standard buffer at 24°C the equilibrium constant is 1x10^13/M, corresponding to a ΔF equal to -18 kcal/mole. From the change in equilibrium constant with temperature, ΔH equals about + 8.5 kcal/mole. Therefore, in terms of heat energy, the binding of repressor to operator is actually unfavorable. The driving force for the reaction comes from the entropy change which equals + 90 cal/mole/deg at 24°C." |