Kinetics of hIL-10 binding to immobilized heparin.

(A) Association and dissociation curves of hIL-10 binding to immobilized biotinylated albumin–heparin. The binding of hIL-10 (13.5-54 nmol/L) was followed in the biosensor until a plateau was reached; after washing, the resultant dissociation was followed (arrow indicates initiation of dissociation). The binding response in response units (arc seconds) was recorded as a function of time and showed the association phase (A), the equilibrium (E), and the dissociation phase (D). Three separate sets of binding reactions were performed in duplicate for each hIL-10 concentration, of which one is illustrated (top panel). Association profiles are shown for all 4 concentrations, whereas only the dissociation profile for the highest concentration is shown for clarity. (B) Plot of the observed on rate (k_on) values against hIL-10 concentration yields a straight line (r = 0.991). The slope of the line corresponds to the association rate constant, k_a(3.44 ± 0.19 × 10⁵ mol/L⁻¹S⁻¹). The dissociation rate constant,k_d (0.019 ± 0.001 S⁻¹) is given by the intercept. In this specific example, the resultantK_d is 54 ± 7 nmol/L.