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Characterization of IgG Receptors of the Fetal Rabbit Yolk SAC Membrane: Localization to Subcellular Fraction and Effects of Chemical Agents and Enzymes on Binding¹

From the Department of Biochemistry, The University of Texas System Cancer Center, M. D. Anderson Hospital and Tumor Institute, Houston, Texas 77030 and The Health Science Center, Graduate School of Biomedical Sciences, Houston, Texas 77030

Abstract

Previous studies have established the existence of IgG receptors on the endodermal cells of the fetal rabbit yolk sac membrane (YSM). The present study partially characterizes these cell-associated receptors. The specific binding of rabbit IgG (IgG_R) to freshly prepared cell homogenates, nuclei-free brush border preparations, and plasma membrane-rich fractions confirms that receptor function is associated with the endodermal cell, and indicates that this function is localized on its apical brush border, specifically on its plasma membrane. The protein nature of the receptor is demonstrated by the loss of specific binding capacity after treatment of formalin-fixed YSM with papain and trypsin. Evidence has also been adduced which indicates that membrane carbohydrate is not involved in receptor function. Thus, treatment of YSM with neuraminidase, -galactosidase, mixed glycosidases, as well as oxidation of YSM with periodate all are without effect on its capacity to bind IgG_R. The interaction of IgG_R with the receptor elements of formalin-fixed YSM is partially ionic in character. NaCl reversibly inhibits binding of IgG_R by 60%. Divalent ions such as Ca⁺⁺ are not involved in this receptor-ligand interaction since EDTA-treated YSM binds IgG_R to the same extent as do controls. Receptor material on fixed YSM resists extraction by non-ionic detergents, deoxycholate, and chaotropic agents.

Footnotes

¹ This work was supported in part by Grant HD7752 from The National Institutes of Health.

² Please send reprint requests to Dr. Max Schlamowitz, Department of Biochemistry, University of Texas System Cancer Center, M. D. Anderson Hospital and Tumor Institute, 6723 Bertner Avenue, Houston, Texas 77030.