Rate equations for two-state conformational change

Let us assume that the kinetic scheme for a simple two-state conformational transition is 

Stochastic biochemical systems and the chemical master equation 

Unimolecular reactions such as this one involve conformational changes of a single molecule without explicit interaction with other molecules. Implicit interactions with the solvent, of course, are assumed. As for the generic master equation introduced above, rather than asking the question What is the concentration of species A at time / . we ask What is the probability that a single molecule is in state A at time tl  

For this simple two-state transition, the traditional deterministic chemical kinetics (see Chapter 3) is based on rate equations for the concentration of A  

If we are dealing with a finite number N of E molecules in a cell, and the number is small enough that fluctuations are expected to be significant, then clearly we need to modify the Equation (11.6) in two crucial ways. First, the species A must now be measured in discrete numbers ha rather than continuous concentration [A], Second, we recognize that ha has a probability distribution 

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