Energy-Transducing Molecular Machines

Starting from the extended statement of the Second Law (that includes the characteristic time of molecular processes), McClare [3-6] deduced that there are two general ways of obtaining useful work from the chemical reactions  

Independently of McClare, similar ideas have been put forward by one of us [1, 2] who elaborated on the concept of molecular machines for enzyme catalysis and energy transduction in chemical and biochemical systems. A central point of this concept was founded on the notion of the crucial role of the conformational relaxation of biopolymers in catalyzing biochemical processes. We will consider the application of this relaxation concept to enzymo-logy and bioenergetics in Chapters 4 and 5. We now focus our attention on the general principles of energy transduction by molecular machines. 

Isothermal expansion of an ideal gas inside a cylinder with a traveling piston (Fig. 3.1) represents a typical step of the simplest macroscopic machine. Gas molecules are confined to the constraining part of the machine (cylinder), and the functioning of this device is associated with the movement of its mobile part (piston) corresponding to its traverse along one selected 

Let us consider one step of the functional cycle of a mechanical entropic machine—expansion of an ideal gas confined to a cylinder with a movable piston (Fig. 3.1). The external load M applied to the top of the piston is assumed to be initially equilibrated by the gas pressure, p = nRT/V, where V is the initial volume of gas in the cylinder, T is the gas temperature in degrees Kelvin, R is the universal gas constant, and n is the number of moles of the gas. The system is assumed to be in contact with a thermostat. On gradually reducing the weight of the external load from to M2, gas will expand, lifting the load and thus performing mechanical work, AW. If the motion of a piston occurs slowly enough, the temperature of the gas will remain con- 

Energy-Transducing Devices and the Problem of the Optimal Functioning of Molecular Machines 

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