text: For an enzyme immobilised on an electrode, the value of the current at a certain potential equates , where  is the number of electrons exchanged in the catalytic reaction,  is the electrode surface,  is the electroactive coverage, and TOF is the turnover frequency (or "turnover number"), that is, the number of substrate molecules transformed per second and per molecule of adsorbed enzyme).The latter can be deduced from the absolute value of the current only on condition that  is known, which is rarely the case.  However, information is obtained by analysing the relative change in current that results from changing the experimental conditions.
  The factors that may influence the TOF are (i) the mass transport of substrate towards the electrode where the enzyme is immobilised (diffusion and convection), (ii) the rate of electron transfer between the electrode and the enzyme (interfacial electron transfer), and (iii) the "intrinsic" activity of the enzyme, all of which may depend on electrode potential.
  The enzyme is often immobilized on a rotating disk working electrode (RDE) that is spun quickly to prevent the depletion of the substrate near the electrode. In that case, mass transport of substrate towards the electrode where the enzyme is adsorbed may not be influential.