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Biogenesis of hepatocyte plasma-membrane domains. Incorporation of (3H)fucose into plasma-membrane and golgi-apparatus glycoproteins.

ABSTRACT: 1. Rats were injected intracaudally with [3H]fucose and its rate of incorporation into the fucoproteins of serum, Golgi and plasma-membrane subfractions was followed for up tp 2h. 2. Incorporation into the Golgi dictyosome and secretory-vesicular fractions reached a maximum at 15 min or less, but most of the radioactivity was associated with classes of secretory glycoproteins. Incorporation into sinusoidal plasma-membrane fractions reached a maximum at 30 min, coinciding with the maximum release of fucoproteins into the serum. Contiguous and canalicular plasma-membrane fractions were labelled slightly later and at a lower rate and specific radioactivity. 3. Fluorography of fucoproteins separated by polyacrylamide-gel electrophoresis helped to distinguish between the major secretory and membrane-bound glycoproteins. The results show that a major biogenetic sequence is probably from Golgi dictyosomes to Golgi secretory elements to a sinusoidal plasma membrane. 4. The kinetics of incorporation make it unlikely that there is rapid and direct insertion of glycoproteins into the bile-canalicular plasma membrane. A route involving direct transfer of glycoproteins via a membrane-mediated intracellular path from the blood sinusoidal to the bile-canalicular plasma membranes is proposed.

SUBMITTER: Evans WH

PROVIDER: S-EPMC1162416 | biostudies-other | 1980 Dec

REPOSITORIES: biostudies-other

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Project description:The biogenesis of plasmalemma glycoproteins of rat small-intestinal villus cells was studied by following the incorporation of l-[1,5,6-(3)H]fucose, given intraperitoneally with and without chase, into Golgi, lateral basal and microvillus membranes. Each membrane fraction showed distinct kinetics of incorporation of labelled fucose and was differently affected by the chase, which produced a much greater decrease in incorporation of label into Golgi and microvillus than into lateral basal membranes. The kinetic data suggest a redistribution of newly synthesized glycoproteins from the site of fucosylation, the Golgi complex, directly into both lateral basal and microvillus membranes. The observed biphasic pattern of label incorporation into the microvillus membrane fraction may be evidence for a second indirect route of incorporation. The selective effect of the chase suggests the presence of two different pools of radioactive fucose in the Golgi complex that differ in (1) their accessibility to dilution with non-radioactive fucose, and (2) their utilization for the biosynthesis of membrane glycoproteins subsequently destined for either the microvillus or the lateral basal parts of the plasmalemma. The radioactively labelled glycoproteins of the different membrane fractions were separated by sodium dodecyl sulphate/polyacrylamide-slab-gel electrophoresis and identified by fluorography. The patterns of labelled glycoproteins in Golgi and lateral basal membranes were identical at all times. At least 14 bands could be identified shortly after radioactive-fucose injection. Most seemed to disappear at later times, although one of them, which was never observed in microvillus membranes, increased in relative intensity. All but two of the labelled glycoproteins present in the microvillus membrane corresponded to those observed in Golgi and lateral basal membranes shortly after fucose injection. The patterns of labelled glycoproteins in all membrane fractions were little affected by the chase. These data support a flow concept for the insertion of most surface-membrane glycoproteins of the intestinal villus cells.

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Biogenesis of hepatocyte plasma-membrane domains. Incorporation of (3H)fucose into plasma-membrane and golgi-apparatus glycoproteins.

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