Why Does the Human Body Maintain a Constant 37-Degree Temperature?: Thermodynamic Switch Controls Chemical Equilibrium in Biological Systems

Applying the Planck-Benzinger methodology to biological systems, we have established that the negative Gibbs free energy minimum at a well-defined stable temperature, ⟨ T S ⟩, where the bound unavailable energy T Δ S ° = 0, has its origin in the sequence-specific hydrophobic interactions. Each such system we have examined confirms the existence of a thermodynamic molecular switch wherein a change of sign in [Δ C p °] reaction leads to a true negative minimum in the Gibbs free energy change of reaction, and hence a maximum in the related equilibrium constant, K eq . At this temperature, ⟨ T S ⟩, where Δ H °( T S )(-) = Δ G °( T S )(-) min , the maximum work can be accomplished in transpiration, digestion, reproduction or locomotion. In the human body, this temperature is 37°C. The ⟨ T S ⟩ values may vary from one living organism to another, but the fact that the value of T Δ S °( T ) = 0 will not. There is a lower cutoff point, ⟨ T h ⟩, where enthalpy is unfavorable but entropy is favorable, i.e. Δ H °( T h )(+) = T Δ S °( T h )(+), and an upper limit, ⟨ T m ⟩, above which enthalpy is favorable but entropy is unfavorable, i.e. Δ H °( T m )(−) = T Δ S °( T m )(−). Only between these two temperature limits, where Δ G °( T ) = 0, is the net chemical driving force favorable for such biological processes as protein folding, protein-protein, protein-nucleic acid or protein-membrane interactions, and protein self-assembly. All interacting biological systems examined using the Planck-Benzinger methodology have shown such a thermodynamic switch at the molecular level, suggesting that its existence may be universal.