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J.Health Sci., 55(4), 636-640, 2009
In Vitro Binding Assay of 31Methionine-oxidized Cholecystokinin Octapeptide to the CCKB Receptor
Hideaki Ichiba, Mio Nakamoto,
Takehiko Yajima, and Takeshi Fukushima*
Department of Analytical Chemistry, Faculty of Pharmaceutical Sciences, Toho University, 2-2-1 Miyama, Funabashi-shi, Chiba 274-8510, Japan
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.
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