Biosynthesis and transport of glycoproteins in the small intestinal epithelium of rats: I. Developmental change and effect of hypophysectomy |
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Authors: | Kwo-yih Yeh Florence Moog |
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Institution: | 2. Chemotherapy Research Department, Southern Research Institute, Birmingham, Alabama 35255 USA;3. Department of Biology, Washington University, St. Louis, Missouri 63130 USA |
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Abstract: | The biosynthesis and intracellular transport of glycoproteins in duodenal absorptive cells of intact rats at 6 and 24 days and hypophysectomized rats at 24 days of age were studied after 20 min intralumenal pulse-labeling of d-3H]galactose, l-3H]fucose, or d-3H]mannose. Autoradiographic studies showed that the incorporation of sugars increased significantly in intact rats between 6 and 24 days. When rats were hypophysectomized at 6 days of age, the intestinal epithelium at 24 days incorporated d-3H]galactose at a level significantly lower than that of intact rats at 24 days. Hypophysectomy also interfered with the developmental increase in d-3H]mannose, but not in l-3H]fucose, incorporation. Biochemical study indicated that the radioactivity in the lipid-free acid-precipitable glycoproteins in the intestine of 24-day-old intact rats at 20 min after d-3H]galactose injection was 129% and 97% higher than that in 6-day-old rats and in 24-day-old hypophysectomized rats, respectively. The patterns of intracellular transport of newly synthesized galactosylated or fucosylated glycoproteins in all animal groups were similar; the labeled glycoproteins were initially present in the Golgi and were transported through the smooth endoplasmic reticulum to either the lateral membrane or the brush-border membrane within 60 min after the injection of labeled sugars. The proportion of labeled glycoproteins that migrated to the brush-border membrane, however, increased about twofold in the intact rats between 6 and 24 days of age at 60–240 min after d-3H]galactose injection. Hypophysectomy interfered with developmental increase in the transport of glycoproteins from the apical cytoplasm to the brush-border membrane. It was concluded that the incorporation of monosaccharide precursors into glycoproteins and the porportion of newly synthesized galactosylated or fucosylated glycoproteins transported to the brush-border membrane increase during postnatal development. The developmental changes are regulated, at least partially, by the pituitary gland. |
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Keywords: | Address requests for reprints to: Dr Kwo-yih Yeh Division of Gastroenterology S & R 12 St Luke's-Roosevelt Hospital Amsterdam Avenue at 114th Street New York NY 10025 |
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