Figure 3. Formation of UB-221–IgE complexes in PBS and human serum.

A study of UB-221–IgE complex formation in PBS solution and human serum was conducted using fluorescence detection system–analytical ultracentrifugation (FDS-AUC), in which the Alexa Fluor 488–conjugated UB-221 was used as a marker. The human IgE and UB-221 were mixed in PBS and serum at a dynamic range of molar ratios from 1:1 through 1:10, and the formed complexes were analyzed by FDS-AUC as described in the Methods. The overall results of FDS-AUC suggest that a molar excess of either UB-221 or IgE would result in the formation of smaller complexes, while the largest complexes are formed at an equimolar ratio; the presence of UB-221–IgE complexes in an equimolar ratio at x:y or y:x (e.g., 1:3 or 3:1) would produce a similar complex pattern; and complex profiles in PBS and serum are similar, except that broadening peaks are seen associated with serum samples likely due to higher viscosity and other physicochemical mechanisms. C(S) represents the sedimentation coefficient distribution values with 68% confidence level; S_20,W(S) represents the apparent sedimentation s-values that were converted to s20,W using density and viscosity of the buffer solutions measured on densitometer and viscometer.