Supporting Text Dimer Dissociation Constant in Vitro and in Vivo

The dimer dissociation constant Kd is defined as the ratio of the concentrations of the monomers ( p1 ) and dimers ( p2 ) in steady state, i.e., Kd = p1 2 p2 . In terms of the basic kinetic parameters (the association rate ka and the dissociation rate kd ), the in vitro dissociation constant is simply Kd (0) = kd ka . However, the effective value of Kd is modified in vivo due to a variety of processes, including those that change the rate constants k. Even if the rate constants do not change, Kd will also be affected by proteolysis or dilution, which alter the steady-state cellular protein concentrations. In the latter case, the combined effects of all these processes can be described at the level of chemical kinetics by the equations dp1 dt = S − λp1 ⋅ p1 − 2ka p1 2 + 2kd p2 [5]