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ENZYME-STRUCTURE RELATIONSHIPS IN THE ENDOPLASMIC RETICULUM OF RAT LIVER : A Morphological and Biochemical Study
L Ernster1, P Siekevitz, G E Palade
1The Rockefeller Institute, New York, and The Wenner-Gren Institute, University of Stockholm, Stockholm, Sweden.
The Journal of Cell Biology
|October 30, 2009
Summary
Researchers isolated rat liver microsome components, separating membrane-bound enzymes from soluble ones. This reveals distinct localization and organization of endoplasmic reticulum enzymes.
Area of Science:
- Biochemistry
- Cell Biology
- Molecular Biology
Background:
- Rat liver microsomes are complex structures containing various enzymes essential for cellular functions.
- Understanding the localization and organization of these enzymes within the endoplasmic reticulum is crucial for comprehending cellular metabolism and function.
Purpose of the Study:
- To investigate the distribution and binding characteristics of enzymes within rat liver microsomes.
- To differentiate between membrane-bound and soluble enzymes in the endoplasmic reticulum.
- To elucidate the enzymic organization of the endoplasmic reticulum based on enzyme localization.
Main Methods:
- Subfractionation of rat liver microsomes using sodium deoxycholate.
- Isolation of a membrane fraction rich in phospholipids and specific enzymes.
- Separation of soluble enzymes and ribonucleoprotein particles in the supernatant fraction.
- Enzyme activity assays for NADH-cytochrome c reductase, NADH diaphorase, glucose-6-phosphatase, ATPase, NADPH-cytochrome c reductase, and cytochrome b5.
Main Results:
- A membrane fraction was isolated, enriched with phospholipids and enzymes like NADH-cytochrome c reductase, glucose-6-phosphatase, and ATPase.
- Soluble fractions contained NADPH-cytochrome c reductase and cytochrome b5.
- Ribonucleoprotein particles were largely devoid of the studied enzyme activities.
- Membrane-bound enzyme activity varied with microsomal structural state, while soluble enzymes remained stable.
Conclusions:
- Certain endoplasmic reticulum enzymes are tightly bound to membranes, while others are loosely bound or soluble within the lumen.
- This differential localization suggests distinct roles and organizational principles for enzymes within the endoplasmic reticulum.
- The findings provide insights into the structural and functional organization of the endoplasmic reticulum.
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