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Role of the Carbohydrate Residues of Human Chorionic Gonadotropin in Binding and Stimulation of Adenosine 3',5'-Monophosphate Accumulation by Porcine Granulosa Cells^*

Department of Physiology, University of Maryland School of Medicine Baltimore, Maryland 21201
the Division of Cell and Molecular Biology, State University of New York at Buffalo Buffalo, New York 14214

Address requests for reprints to: Dr. Cornelia P. Channing, University of Maryland School of Medicine, Department of Physiology, 660 West Redwood Street, Baltimore, Maryland 21201.

Abstract

Removal of the sugar residues internal to sialic acid from the hCG molecule markedly diminished the ability of hCG to stimulate cAMP accumulation by porcine granulosa cells during a 30-min incubation period. At the same time, removal of sugars internal to sialic acid enabled the resulting hCG derivatives to become competitive inhibitors of hCG stimulation of cAMP accumulation. This contrasts with the finding that removal of sugars internal to sialic acid residues has a lesser effect on the ability of hCG to inhibit the binding of human [¹²⁵I]iodo-CG to granulosa cells, provided the hCG derivatives were added before the tracer. It would, therefore, seem that hCG with sugars internal to sialic acid removed is able to bind to the receptor, but that, once bound, it is unable to activate adenylate cyclase. Under these conditions, it can also act as a competitive inhibitor of hCG stimulation of cAMP accumulation.

Footnotes

^* This work was supported by Research Grants HD-08466, HD-08834 (C.P.C.), and HD-08766 (O.P.B.) from the NICHHD, USPHS. It was presented in part at the Annual Meeting of the FASEB held in Anaheim, CA, April, 1976 (Abstract 3268).

Received November 3, 1976.

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