[Application of γ imaging in chromatographic separation and protein molecular site density determination]

We in this study measured the site density of E-selectin in order to explore the practical pliability using radionuclide labeling method and γ-imaging of single photon emission computer tomography (SPECT). This method required labeling of antibody with ¹²⁵I using Indogen method and binding of the labeled antibody to E-selectin. Labeled E-selectin was separated and purified in a Sephadex G25 column. The different fractions of the eluants were imaged, analyzed and quantified with SPECT method. For measuring the saturation curve of E-selectin, 130 μL of E-selectin solution with different concentrations were added in a 48-well plate and incubated overnight at 4℃. After incubation, 130 μL of labeled antibody solution were added and kept incubated for 30 min. The resulted mixture was washed, and the radioactivity in each sample was detected by SPECT. The levels of radioactivity were translated to site densities, and were used to plot a standard curve. The labeled product was quantitatively analyzed with SPECT. The labeling rate of E-selectin was 78%. The saturation curve of different concentration samples showed that when the concentration was in the concentration range of 0-1 mg/mL, the standard curve was y=6 045.7 x-51.166, R²=0.997 9. Based on this finding, it could be concluded that γ-imaging is an important tool for analysis of radiolabeled product and determination of site density.