A motor enzyme is a thermal turbine. It no more causes a motor’s trajectory (enzymes do not cause a reaction flux) than a wind turbine causes wind. A chemical flux down a macroscopic chemical gradient, ΔQ, turns a motor enzyme’s passive reaction cycle to perform mechanical work, ΔPE. We have directly observed that the thermal turbine of muscle is the probability density—not the sum—of its motor enzyme parts. That is, muscle’s thermal turbine is entropy, TS. We have shown that muscle cyclically changes its form, TΔS, when it absorbs ΔQ and performs work, ΔPE. This is precisely the mechanism described by the second law of thermodynamics. TΔS = ΔQ + ΔPE.This one equation (a.k.a., the Gibbs free energy equation) describes energy transduction by all thermal turbines (thermal ratchets, molecular motors, chemical reactions, muscle, steam engines, etc.). I show that it defines irreversible chemical kinetics and thermodynamics on every scale from muscle to myosin motors all the way down to electrons in a magnetic field. I show that the kinetic theory of gases, chemical kinetic theory, Boltzmann’s distribution, Gibbs’ chemical potentials, and the Crooks fluctuation theorem are all microscopic approximations of the macroscopic causal relationships defined by this one equation.
Josh E. Baker (Sun,) studied this question.