where 𝐽 is the diffusion flux of the substrate from the solution to the enzymatic thin layer where it is enzymatically consumed with an overall rate of conversion per unit of enzymatic surface, i.e. of electrode surface, denoted 𝑟𝑎𝑡𝑒 . Denoting [𝐸] the immobilized enzyme concentration, 𝐾 = (𝑘 + 𝑘 )/𝑘 the usual "Michaelis constant" and [𝑆] the mean substrate concentration within the enzyme layer (Scheme 1), one has: