Segregated and random mixing models make distinguishable predictions. (A) Schematic of sequential digestion of N termini of β2 and β3a associated channels for assembly in accordance with segregated model. (B) Sequential digestion of N termini (f_ss) in accordance with random mixing assembly model. (C) Predicted time course of removal of inactivation for the segregated model for the indicated changes in the β2/(β3a+β2). (D) Predicted time course of removal of inactivation for random mixing model. (E) Relationship of fractional changes in slow tail current amplitude (A_ST) with fraction of non-inactivating current (f_ss) during trypsin-dependent removal of N termini for segregated model. (F) Tail current vs. f_ss relationship for digestion in accordance with random mixing model.