Under very oxidising or very reducing conditions, the steady-state catalytic current sometimes tends to a limiting value (a plateau) which (still provided there is no mass transport limitation) relates to the activity of the fully oxidised or fully reduced enzyme, respectively. If interfacial electron transfer is slow and if there is a distribution of electron transfer rates (resulting from a distribution of orientations of the enzymes molecules on the electrode), the current keeps increasing linearly with potential instead of reaching a plateau; in that case the limiting slope is proportional to the turnover rate of the fully oxidised or fully reduced enzyme.
The change in steady-state current against potential is often complex (e.g. not merely sigmoidal).