Figure 4. Affinity kinetics between human ghrelin and IgG assayed by SPR.

Affinity kinetics were analysed by the Langmuir’s 1:1 model fit on five serial dilutions of IgG from 0.5 mg ml⁻¹ and flow speed of 30 μl min⁻¹. Representative examples of curve fits for the affinity kinetic analysis of a control subject (a), AN (b) and obese (c) patients. The affinity kinetics parameters of the given examples are the following: (a) small k_a (±s.e.m.), 9.17 × 10³±1.09 × 10² M⁻¹ s⁻¹, small K_d (±s.e.m.), 1.37 × 10⁻³±3.14 × 10⁻⁵ s⁻¹, KD, 1.50 × 10⁻⁷ M, χ² 21.1; (b) small K_a (±s.e.m.), 8.76 × 10³±1.17 × 10² M⁻¹ s⁻¹, small K_d (±s.e.m.), 1.78 × 10⁻³±3.52 × 10⁻⁵ s⁻¹, KD, 2.03 × 10⁻⁷ M, χ² 13.7 and (c) small K_a (±s.e.m.), 1.71 × 10⁴±2.53 × 10² M⁻¹ s⁻¹, small K_d (±s.e.m.), 1.77 × 10⁻³±3.98 × 10⁻⁵ s⁻¹, KD, 1.04 × 10⁻⁷ M, χ² 12.3. Affinity for ghrelin of IgG in obese patients was increased compared to controls and AN patients as represented by lower mean K_D values in obese (d). Association (K_a) and dissociation (K_d) rates are shown in (e) and (f), respectively. (d) K–W test, P=0,004, Dunn’s **P<0.01 AN versus obese, Student’s t-test **P<0.01 controls versus obese; (e) K–W test, P=0.03, Dunn’s *P<0.05; (f) K–W test, P=0,034, Dunn’s *P<0.05 controls versus AN, M–W test, *P<0.05 AN versus obese. (Contr. n=14, AN n=12 and obese n=14, error bars, s.e.m.).