Biophys J, January 2000, p. 416-429, Vol. 78, No. 1

A Thermodynamic Molecular Switch in Biological Systems: Ribonuclease S' Fragment Complementation Reactions

Department of Biochemistry and Molecular Biology, University of Florida College of Medicine, Gainesville, Florida 32610-0245 USA

It is well known that essentially all biological systems function over a very narrow temperature range. Most typical macromolecular interactions show H°(T) positive (unfavorable) and a positive S°(T) (favorable) at low temperature, because of a positive (Cp°/T). Because G°(T) for biological systems shows a complicated behavior, wherein G°(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 Cp°(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 H°(T), S°(T), W°(T), and G°(T) give rise to the classically observed behavior patterns in biological reactivity, as may be seen in ribonuclease S' fragment complementation reactions.

Biophys J, January 2000, p. 416-429, Vol. 78, No. 1
© 2000 by the Biophysical Society   0006-3495/00/01/416/14  $2.00

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