3033154

Glycoprotein as a constituent of purified gamma-aminobutyric acid/benzodiazepine receptor complex: structures and physiological roles of its carbohydrate chain.

Article date: 1987/6/1

PubMed ID: 3033154

Journal name: Journal of neurochemistry (ISSN: 0022-3042)

ABSTRACT

The effect of treatments with various enzymes and chemically modifying agents on [3H]muscimol binding to a purified gamma-aminobutyric acid (GABA)/benzodiazepine receptor complex from the bovine cerebral cortex was examined. Treatments with pronase, trypsin, guanidine hydrochloride, and urea significantly decreased the binding of [3H]muscimol, but dithiothreitol, N-ethylmaleimide, reduced glutathione, oxidized glutathione, cysteine, and cystine had no significant effect. These results indicate that the GABA receptor indeed consists of protein, but -SH and -S-S- groups in the protein are not involved in the exhibition of the binding activity. On the other hand, column chromatography using concanavalin A-Sepharose eluted protein having [3H]muscimol binding activity and staining of glycoprotein using an electrophoresed slab gel indicated the existence of two bands originating from the subunits of the GABA/benzodiazepine receptor complex. Furthermore, treatments with various glycosidases such as glycopeptidase A, beta-galactosidase, and alpha-mannosidase significantly increased the binding of [3H]muscimol. These results strongly suggest that GABA/benzodiazepine receptor complex is a glycoprotein and that its carbohydrate chain may be a hybrid type. Treatment with beta-galactosidase resulted in the disappearance of the low-affinity site for [3H]muscimol binding and in an increase of Bmax of the high-affinity site, without changing the KD value. These results suggest that the carbohydrate chain in the receptor complex may have a role in exhibiting the low-affinity binding site for GABA. The observation that the enhancement of [3H]muscimol binding by treatments with beta-galactosidase and glycopeptidase A were much higher than that with alpha-mannosidase may also indicate a special importance of the beta-galactosyl residue in the inhibition of GABA receptor binding activity.(ABSTRACT TRUNCATED AT 250 WORDS)

This document is available from: http://directlinks.cc/files/muscimol/3033154.pdf

Author List: Kuriyama K, Taguchi J

Publication Types: Journal Article; Research Support, Non-U.S. Gov't

Substances mentioned in the article: Glycoproteins; Receptors, GABA-A; Muscimol; Glycoside Hydrolases; Endopeptidases;

Mesh terms: Animals; Cattle; Cerebral Cortex/metabolism; Chromatography; Electrophoresis, Polyacrylamide Gel; Endopeptidases/pharmacology; Glycoproteins/analysis; Glycoside Hydrolases/pharmacology; Molecular Weight; Muscimol/metabolism; Receptors, GABA-A/drug effects;

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