The biosynthesis, assembly and secretion of vitellogen, a high mol.wt. multicomponent
The biosynthesis, assembly and secretion of vitellogen, a high mol.wt. multicomponent
The process by which the eggs-yolk protein precursor vitellogenin is biosynthesized, assembled and secreted has been. studied. This protein has been previously characterized as a Ca2i-binding glycolipophosphoprotein with a mol. wt. of 450,000 - 500,000 and is ':biosynthesized by Xenopus laevis liver in response to 173 -oestradiol. It has also been previously shown that vitellogenin contains within its structure the two egg-yolk proteins, lipovitellin(140,000 in mol.wt.) and phosvitin (35,000 in mol.wt.).Evidence is presented which shows that the microsomes synthesize precursors of vitellogenin. These precursors were solubilized from the membranes with detergent and analysed by SDS polyacrylamide gel electrophoresis. This analysis indicated that there is only one precursor polypeptide and this has a mol. wt. of 200,000 This demonstrates that the egg-yolk proteins are.. biosynthesized as part of this larger polypeptide. Experiments also demonstrate the' 1existence of a microsomal protease which is able to cleave the precursor into, smaller fragments. The nature of these fragments has provided some indirect evidence that phosvitin and lipovitellin ' light crbpin are situated together within the precursor molecule.This precursor data fits in well with structural studies on vitellogenin, since it has been confirmed here that the native protein consists,of two identical subunits each with a mol.wt. of i200,000, It has also been shown that trypsin or chymotrypsin can cleave this subunit species into a leucine-rich fragmentt which resembles lipovitellin anUa serine-rich fragment which at best is similar to phosvi.tin but also contains 8 timee more leucine than the authentic phoavitin molecule. Pulse-chase experiments demonstrate that the crosomal precursor of vitellogenin is compartmentalized within the microsomes throughout its intracellular phase and that during its translocation to the plasma membrane it is transported from the rough to the smooth membranes. Deoxycholate subfractionation of the microsomes indicates that the translocation occurs along the intraoisternae space of the endoplasmic reticulum. The intracellular transport of vitellogenin would thus appear to be a membrane-dependent process. Other experiments indicate that the oestrogen induced lipid and cholesterol biosynthesis occuring in hepatocytes before they become maximally vitellogenic is directed mainly towards the provision of new membranes; it is thus proposed that when oestrogen reduces Xenopu hepatocytes to re-differentiate to produce-large quantities of egg-yolk protein precursors there is a coordinated increase in microsomal membrane biosynthesis.
University of Southampton
1976
Penning, Trevor Martin
(1976)
The biosynthesis, assembly and secretion of vitellogen, a high mol.wt. multicomponent.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
The process by which the eggs-yolk protein precursor vitellogenin is biosynthesized, assembled and secreted has been. studied. This protein has been previously characterized as a Ca2i-binding glycolipophosphoprotein with a mol. wt. of 450,000 - 500,000 and is ':biosynthesized by Xenopus laevis liver in response to 173 -oestradiol. It has also been previously shown that vitellogenin contains within its structure the two egg-yolk proteins, lipovitellin(140,000 in mol.wt.) and phosvitin (35,000 in mol.wt.).Evidence is presented which shows that the microsomes synthesize precursors of vitellogenin. These precursors were solubilized from the membranes with detergent and analysed by SDS polyacrylamide gel electrophoresis. This analysis indicated that there is only one precursor polypeptide and this has a mol. wt. of 200,000 This demonstrates that the egg-yolk proteins are.. biosynthesized as part of this larger polypeptide. Experiments also demonstrate the' 1existence of a microsomal protease which is able to cleave the precursor into, smaller fragments. The nature of these fragments has provided some indirect evidence that phosvitin and lipovitellin ' light crbpin are situated together within the precursor molecule.This precursor data fits in well with structural studies on vitellogenin, since it has been confirmed here that the native protein consists,of two identical subunits each with a mol.wt. of i200,000, It has also been shown that trypsin or chymotrypsin can cleave this subunit species into a leucine-rich fragmentt which resembles lipovitellin anUa serine-rich fragment which at best is similar to phosvi.tin but also contains 8 timee more leucine than the authentic phoavitin molecule. Pulse-chase experiments demonstrate that the crosomal precursor of vitellogenin is compartmentalized within the microsomes throughout its intracellular phase and that during its translocation to the plasma membrane it is transported from the rough to the smooth membranes. Deoxycholate subfractionation of the microsomes indicates that the translocation occurs along the intraoisternae space of the endoplasmic reticulum. The intracellular transport of vitellogenin would thus appear to be a membrane-dependent process. Other experiments indicate that the oestrogen induced lipid and cholesterol biosynthesis occuring in hepatocytes before they become maximally vitellogenic is directed mainly towards the provision of new membranes; it is thus proposed that when oestrogen reduces Xenopu hepatocytes to re-differentiate to produce-large quantities of egg-yolk protein precursors there is a coordinated increase in microsomal membrane biosynthesis.
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Published date: 1976
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Local EPrints ID: 467208
URI: http://eprints.soton.ac.uk/id/eprint/467208
PURE UUID: e33be97b-1608-48c8-ad71-229340e3c68c
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Date deposited: 05 Jul 2022 08:16
Last modified: 05 Jul 2022 08:16
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Author:
Trevor Martin Penning
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