[I] 0 plot under tight-binding conditions is always ever-so-slightly concave upward. In some cases, depending on the value of K i = k off /k on , there is a prominent minimum. In fact, at extremely low values of K i , the minimum on the plot corresponds to zero k obs value occurring at exactly [I] 0 = [E] 0 . At sufficiently high inhibitor concentrations the k obs plot appears linear with a slope that does not depend on the K i but only on the association rate constant k on .