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DIFFERENTIATION OF ENDOPLASMIC RETICULUM IN HEPATOCYTES : II. Glucose-6-Phosphatase in Rough Microsomes
A Leskes1, P Siekevitz, G E Palade
1The Rockefeller University, New York 10021.
The Journal of Cell Biology
|October 30, 2009
Summary
Glucose-6-phosphatase is evenly distributed throughout the rough endoplasmic reticulum in developing rat hepatocytes. This enzyme localization study confirms uniform distribution within cellular membranes, suggesting molecule-by-molecule insertion of new components.
Area of Science:
- Cell Biology
- Biochemistry
- Developmental Biology
Background:
- Glucose-6-phosphatase is a key enzyme in glucose metabolism.
- Its localization within hepatocytes is crucial for understanding liver function during development.
- Previous studies suggested potential regional differences in enzyme distribution within the endoplasmic reticulum.
Purpose of the Study:
- To determine the precise localization of glucose-6-phosphatase within the rough endoplasmic reticulum of developing rat hepatocytes.
- To confirm whether the enzyme distribution is uniform or regionally differentiated within the endoplasmic reticulum.
- To validate cytochemical findings using a novel subfractionation method.
Main Methods:
- Electron microscope cytochemistry was used for initial localization.
- A new method was developed to subfractionate rough endoplasmic reticulum based on enzyme activity.
- Isopycnic centrifugation on a two-step density gradient separated microsomes with and without glucose-6-phosphatase activity.
Main Results:
- The enzyme glucose-6-phosphatase appears simultaneously in all rough endoplasmic reticulum of a cell, but asynchronously across the cell population.
- Subfractionation of rough microsomes confirmed that the enzyme is evenly distributed throughout the endoplasmic reticulum.
- The proportion of dense microsomes after reaction correlated with the proportion of positively reacting cells at different developmental stages.
Conclusions:
- Glucose-6-phosphatase is uniformly distributed throughout the rough endoplasmic reticulum of hepatocytes.
- There is no regional differentiation within the endoplasmic reticulum regarding this enzyme's presence.
- Membrane components are likely inserted molecule-by-molecule into existing structures, forming a mosaic of old and new molecules.
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