Analysis of the association constants by a 4-D hypercube. (A) Scheme of the 4-D hypercube. The 16 closed states (C0000…C1111) of a HA model are the corners of a 4-D hypercube in which the Kxxxxs denote the 32 edges (x = 0 for an empty subunit, x = 1 for a subunit to be occupied, and x = 1 for a preoccupied subunit). The colored lines indicate liganding of the respective subunits. (B) Virtual equilibrium association constants Z0001…Z1111 (violet lines) specifying the independent parameters.