摘要：Methionine (Met) residues of cholecystokinin octapeptide (CCK8) are easily oxidized to produce Met sulfoxide and/or sulfone of CCK8. In order to investigate the effect of modification at Met of CCK8 for its CCKB receptor, we evaluated the binding affinity of 4 oxidized forms of CCK8 for CCKB receptor expressed in the plasma membrane of LoVo cells, by performing a flow cytometry-based competitive binding assay using fluorescein isothiocyanate (FITC)-labeled CCK8. Oxidative modification of CCK8 at 28Met and 31Met caused to increase its binding affinity. The affinity of 31Met sulfone CCK8 was strongest and was significantly higher (by 20-30%) than that of native CCK8 ( p <0.05). In contrast, the binding affinity of modified CCK8 was attenuated on replacing 31Met with 31Leu, 31Lys, or 31His.
