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Human platelets are known to carry Fc receptors (Fc R), but the binding characteristics between ligands and Fc gamma R has not been well elucidated. In this study, we investigated the binding kinetics of IgG Fc fragments (Fc) to Fc R, the association and dissociation characteristics of the ligands to and from Fc gamma R using enzymatically modified Fc fragment derivatives. Approximately 60 minutes and 90 minutes were needed at 37 degrees C and 22 degrees C, respectively, for complete saturation of the Fc binding sites with horseradish peroxidase-conjugated Fc (HPO-Fc). Heat aggregated IgG (HAG) had a greater affinity for the Fc gamma R than Fc monomers. Additional binding of HAG was observed even after the binding sites were saturated with Fc monomers. This could be explained by different binding sites available only for immune complexes or by the partial dissociation of binding sites saturated with Fc by HAG. Further, we noted partial dissociation of HPO-Fc, when HAG was added after saturation of the binding sites with HPO-Fc. In a subsequent experiment, we compared the relative affinities of chemically or enzymatically modified Fc derivatives for Fc gamma R. HAG, which was used as a model for CIC, had a greater affinity for platelet Fc gamma R than IgG monomer and Fc derivatives. Pepsin-digestion of Fc caused a total loss of its affinity for the Fc gamma R, whereas b-mercaptoethanol-treated Fc fragments demonstrated substantial binding to the Fc gamma R. These results indicate that the pepsin digestion affects the Fc portion and causes a disruption in the area of the Fc which is essential for the recognition by the platelet Fc gamma R. On the other hand, cleavage of disulfide bridges by beta-mercaptoethanol resulted in a marked increase in affinity for the Fc gamma R. On the other hand, enzymatic cleavage of the carbohydrate moieties of Fc did not alter the affinity of Fc fragments for the Fc gamma R, indicating that the carbohydrates play an insignificant role or are not involved in their binding to the Fc gamma R.
K Shido, and
G Ahmad, and
L Hsu, and
M Kamiyama
December 1987,
Thrombosis and haemostasis,
K Shido, and
G Ahmad, and
L Hsu, and
M Kamiyama
October 1981,
Biochemistry,
K Shido, and
G Ahmad, and
L Hsu, and
M Kamiyama
January 1992,
Immunologic research,
K Shido, and
G Ahmad, and
L Hsu, and
M Kamiyama
October 1985,
Molecular immunology,
K Shido, and
G Ahmad, and
L Hsu, and
M Kamiyama
January 1997,
International reviews of immunology,
K Shido, and
G Ahmad, and
L Hsu, and
M Kamiyama
December 1990,
FASEB journal : official publication of the Federation of American Societies for Experimental Biology,
K Shido, and
G Ahmad, and
L Hsu, and
M Kamiyama
May 2009,
Molecular immunology,
K Shido, and
G Ahmad, and
L Hsu, and
M Kamiyama
March 1993,
European journal of immunology,
K Shido, and
G Ahmad, and
L Hsu, and
M Kamiyama
November 1989,
Clinical immunology and immunopathology,
K Shido, and
G Ahmad, and
L Hsu, and
M Kamiyama
January 1997,
International reviews of immunology,
