Mechanochemical cycles

These arguments can be formalized by postulating a mechanochemical cycle for a single subunit within the motor ... 

The mechanism depicted in Fig. 13.9d is only a schematic of the basic mechanochemical cycle. Fundamental chemical transitions such as ATP hydrolysis and ADP release are not depicted because our data do not uniquely locate these transitions. In a simple sequential model, in which each subunit binds ATP, hydrolyzes it, releases products, and steps, before activating the next subunit, these processes are uniquely determined by the simple requirement that ATP is hydrolyzed before products are released. However, in a more complicated kinetic model in which the individual hydrolysis cycles of the identical subunits are interwoven, such as that depicted in Fig. 13.9, there is no longer a single unique position for these important kinetic events. ATP hydrolysis, for example, might occur immediately after the tight binding of each ATP and before the next subunits is active for ATP docking. 

FIGURE 1.2 (A) Mechanochemical cycle of kinesin motors. Along the reaction cycle two... 

The thermodynamic analysis for each step of mechanochemical cycle, summarized in the free energy diagram (Figure 1.2B), allows us to assess the kinesin... 

The stepping motion involving the reaction step D,, - T -> T, - D +, (Figure 1.2) is unarguably the most spectacular motion along the kinesin s mechanochemical cycle. By precisely probing this dynamics, one can understand an issue like how kinesins... 

FIGU RE 1.7 An expanded mechanochemical cycle of kinesin motors that includes the normal cycle (JF stands for forward cycle. A reversal of T cycle would be the backstep induced by an ATP synthesis) and the possibility of (A) backstep induced by ATP hydrolysis (B) and (B) futile cycle (( )). This type of modification of reaction path is plausible to explain the mechanism of kinesin s backstepping. 

The reversible conversion of the system properties caused by the conformational changes is described by the curves having approximately the same shape, irrespeetive of the stimulus nature, Figure 4.11. The plotted curves differ eaeh to another by the amplitude and the frequency of the changes of measured property. Presently, the efforts are focused on the inerease both of amplitude of dimensional changes and developed foree, and shortening of mechanochemical cycle. 

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