Editing Dissociation constant (section)

===Antibodies===
In the specific case of antibodies (Ab) binding to antigen (Ag), usually the term '''affinity constant''' refers to the association constant.
:<chem>
 Ab + Ag <=> AbAg 
</chem>

:<math chem="">
 K_\mathrm{A} = \frac{\left[ \ce{AbAg} \right]}{\left[ \ce{Ab} \right] \left[ \ce{Ag} \right]} = \frac{1}{K_\mathrm{D}} 
</math>

This [[chemical equilibrium]] is also the ratio of the on-rate (''k''<sub>forward</sub> or ''k''<sub>a</sub>) and off-rate (''k''<sub>back</sub> or ''k''<sub>d</sub>) constants. Two antibodies can have the same affinity, but one may have both a high on- and off-rate constant, while the other may have both a low on- and off-rate constant.

:<math chem="">
 K_A = \frac{k_\text{forward}}{k_\text{back}}  = \frac{\mbox{on-rate}}{\mbox{off-rate}}
</math>