Inhibition schemes.

The figure shows three reasonable ways how inactive mutant subunits could inhibit the hexameric assembly. (A) If all subunits were strictly coupled and the activity of each subunit depended on an entirely intact surrounding, any inactive mutant subunit would inhibit all other subunits (scheme 1, full ring cooperativity). (B) If there were only a local effect on the neighboring subunits, only the two neighbors would be inhibited (scheme 2, local influences). (C) The inhibition might be even more specific and directed to only one of the two neighbors (scheme 3, neighbor inhibition). Table 3 was derived from these schemes considering all possible configurations (Fig. 1).Not shown: for the simulation, the affected subunit does not necessarily need to be the neighbor of the mutated subunit but could also lie in the opposing position. Additional schemes not considered here are discussed in the text.