Figure 3.
Subunit exchange schemes of two kinetics models. (A) Scheme of simple bimolecular exchange model. The tetradecamer constitution is expressed by H and D for 12 unswappable subunits, and h and d for two swappable subunits. For simplicity, the exchange reactions, which do not cause intensity change, such as Hhh + Dhh↔f Hhh + Dhh (an italic letter means an exchanging subunit), are not shown. Top, middle, and bottom rows correspond to the α7 tetradecamers with zero, one, and two differently labeled subunit(s), respectively. Typical α7 tetradecamers are drawn on the left and right sides, where the blue and red spheres show h-α7 and d-α7 subunits, respectively. denotes the exchange probabilities in the reactions, where (see text). (B) Extended exchange scheme by the two-step exchange model assuming the transition between active and inactive (∗) states of the swappable α7 subunit. It is a modification of the reaction scheme Hhh + DddH ⇌Hhd + Dhd (boxed with dashed line in panel A) and exemplifies the extension of the model. k13 is the rate constant of the transition.