Thermodynamics of Enzymatic Reactions

The quasi-stationary approximation studied in the previous section allowed us to break the system of chemical reactions in (5.7)-(5.9) into a couple of subsystems that can be analyzed separately  

The interaction of the enzyme E with the substrate X to form the complex Ex  

The synthesis of molecules A from Ex, and their degradation into molecules Y. 

If we view the whole system from a slow dynamics perspective (that of A molecules), we can think of subsystem 1 as having so fast dynamics that it equilibrates instantaneously with the slow changing variables. At the same time, a second subsystem (labeled 2), in which the effects of the fast subsystem are averaged over the fast time scale, becomes apparent. Subsystem 2 corresponds to the synthesis and degradation of A molecules. 

The forthcoming discussion relies upon the assumption that the system is observed at a slow time scale. From this perspective, subsystem 1 corresponds to the chemical reaction analyzed in Chap. 3. That is, r enzyme molecules flip between states E and Ex. The rate with which individual molecules shift to state Ex is kxsnx This rate is constant because we have assumed a constant wa- Cta the other hand, the rate with which an individual enzyme in state Ex flips to state E is ksx- Note that the reaction is not taken into account. The reason 

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