Functioning Mechanism of ATP-Driven Proteins Inferred on the Basis of Water-Entropy Effect

Abstract

There is a class of proteins called “motor proteins” or “protein machineries” which utilizes the ATP hydrolysis cycle: binding of ATP to a protein, hydrolysis of ATP, and dissociation of ADP and Pi from the protein. In the literature, the functioning mechanism of an ATP-driven protein has been discussed using the concept that it does work by utilizing the chemical energy stored in an ATP molecule or the free energy of ATP hydrolysis. In this chapter, we present a completely different view and argue that a protein is involved in an irreversible chemical reaction accompanying a decrease in system free energy, ATP hydrolysis, and during each hydrolysis cycle the protein undergoes a series of structural changes, leading to the exhibition of high function. The force which makes myosin move along F-actin, for example, is generated not by ATP but by water. In particular, the entropic force originating from the translational displacement of water molecules in the system plays a pivotal role. The concept of chemical–mechanical energy conversion is physically irrelevant.