Netsu Sokutei, 32 (2), p. 86, (2004)



Single Molecule Measurements and Energetics of Biological Nanomachine

Movement is a fundamental characteristic of all living things. This biogenic function is attributed to molecular motors in a cell. Molecular motors are mechano-chemical enzymes that generate forces by using chemical energy derived from the hydrolysis reaction of adenosine tri-phosphate (ATP) molecules. Despite a large number of studies on this issue, the mechanism of mechano-chemical energy transduction is still unsolved. In this review, we describe the experimental and theoretical approaches for elucidating the mechanism how kinesin motors generate the unidirectional movement along a microtubule. By use of a novel single-molecule-detection technique, we detected the elementary processes on the sliding movement of single kinesin molecules. Motility analysis has revealed that a stochastic mechanism underlies in the unidirectional movement of kinesin. To explain the energetic aspects of the stochastic movements, we constructed a new phenomenological framework based on non-equilibrium statistical mechanics, and determined the energetic balance in single kinesin molecules. It is indicated that the hydrolysis energy of ATP is effectively used to generate the unidirectional movement. Our experimental and theoretical approaches will help to understand thermodynamics of nano-world.