The Mechanism Of Biomolecular Motors' Unidirectional Movement And The Kinetics Of ATP Hydrolysis

Molecular motors mainly discussed in this dissertation belong to a class of micro-machinery which convert chemical energy into mechanical one (or reverse) by hydrolysis (or sythesis) of ATP. With the advance of the manipulation of single molecule, the motility of molecular motors has became one of the focus of Biophysics since 1990s. Simultaneous observation of binding, hydrolysis (or synthesis) and release of a fluorescent ATP (or ADP), and movement of molecular motor, has provided a chance to reveal the mechanochemical coupling mechanism of molecular motors.Nonprocessive molecular motor such as myosin II, behaves like Brown-ian movement in cell because of its lower duty ratio (2). The two-state ratchet model has been introduced in Chapter 3. The reaction of ATP hydrolysis has been phenomenologically corresponded to an excitation on Brownian motor. Brownian motor will drift in external field, and its drift velocity depends on the strength of chemical excitation. This model relates the drift velocity of Brownain motor to the concentration of ATP, and can be used for theoretical discussion on the mechanochemical coupling mechanism.The behavior of collective motors, such as muscle contraction, is different from that of single motor. Within the frame of two-state ratchet model, the kinetics of ATP hydrolysis for collective motors has been discussed in Chapter 4. The collective motors' cooperative behavior, which is distinguished from single motor, has been displayed.The enzymatics assay of kinesin has revealed that "the application of load has two important effects on the kinesin cycle: it lowers the maxi-mal stepping rate, and it also lowers the effective rate of ATP binding". This can't be explained by either the simple loosely coupled models or the simple tightly coupled one. The two-strong-coupled heads model, a simple "inchworm", has been suggested in Chapter 5, and has reasonably explained above experiment results.As a brief introduction, the motility assays of molecular motors will be reviewed in Chapter 2.