The term "s" in (28) has been employed as a dummy variable, and σ 2 ≡ s 0 2 /K M2 . We will employ a mean-field approach to derive a depletion timescale for the indicator reaction. Let us first assume that we know the depletion timescale for the indicator reaction; we will denote this timescale as T s2 . The mean available enzyme over the time course of the indicator reaction is given by