Release of intestinal surface-membrane glycoproteins associated with enzyme activity by brief digestion with papain

Author:

Forstner Gordon G.1

Affiliation:

1. Gastrointestinal Unit, Department of Medicine, Toronto Western Hospital, and Institute of Medical Science, University of Toronto, Toronto, Ont., Canada

Abstract

Rat intestinal surface-membrane glycoproteins were labelled by intraperitoneal injection of [1-14C]glucosamine 4h before the animals were killed. At this time, density-gradient centrifugation of disrupted brush borders indicated that glycoprotein radioactivity was distributed identically with sucrase, a plasma-membrane marker. Labelled brush borders were digested by papain for brief time-intervals known to release surface-enzyme particles without disruption of the unit membrane. Digestion for 5min released 90% of the surface sucrase, and almost one-half of the brush-border glycoprotein and label. On Sepharose 4B column chromatography most of the glycoprotein and label emerged as a single peak. This peak contained the most actively labelled glycoprotein in the brush border and was closely associated with maltase, sucrase, β-naphthylamidase and alkaline phosphatase. The peak was partially resolved on polyacrylamide-gel electrophoresis into three bands. Each band contained a distinctive enzyme or enzyme pair, and was labelled by [1-14C]glucosamine. No periodic acid–Schiff-negative protein was observed in the peak material. Glycoproteins susceptible to brief digestion with papain are therefore closely linked to released surface-enzyme particles. Intestinal surface glycoproteins are heterogeneous with respect to molecular weight, electrophoretic mobility and function.

Publisher

Portland Press Ltd.

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1. Mechanisms of Association of Bacteria with Mucosal Surfaces;Ciba Foundation Symposium 80 - Adhesion and Microorganism Pathogenicity;2008-05-30

2. The Differentiation and Redifferentiation of the Intestinal Epithelium and its Brush Border Membrane;Ciba Foundation Symposium 70 - Development of Mammalian Absorptive Processes;2008-05-30

3. Differential mechanisms of induction of ornithine decarboxylase in rat intestine by l- and d-amino acids;Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression;1992-01

4. Functional Morphology of Epithelium of the Small Intestine;Comprehensive Physiology;1991-12

5. Characterisation of the binding sites for Escherichia coli heat-labile toxin type I in intestinal brush borders;Biochimica et Biophysica Acta (BBA) - General Subjects;1991-10-10

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