Related Experiment Video

Updated: Jun 19, 2026

Three-dimensional Characterization of Interorganelle Contact Sites in Hepatocytes using Serial Section Electron Microscopy
09:12

Three-dimensional Characterization of Interorganelle Contact Sites in Hepatocytes using Serial Section Electron Microscopy

Published on: June 9, 2022

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
PubMed

Insights

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.

More Related Videos

Visualization of Endoplasmic Reticulum Subdomains in Cultured Cells16:43

Visualization of Endoplasmic Reticulum Subdomains in Cultured Cells

Published on: February 18, 2014

Study of Endoplasmic Reticulum and Mitochondria Interactions by In Situ Proximity Ligation Assay in Fixed Cells09:34

Study of Endoplasmic Reticulum and Mitochondria Interactions by In Situ Proximity Ligation Assay in Fixed Cells

Published on: December 10, 2016

Related Concept Videos

The Endoplasmic Reticulum01:43

The Endoplasmic Reticulum

The endoplasmic reticulum or ER makes up for more than half of the membranes in a cell and accounts for 10% of total cell volume. It is also the primary protein and lipid synthesis factory for most cell organelles, such as the Golgi apparatus, lysosomes, secretory vesicles, and the plasma membrane. Despite being the most extensive and functionally complex subcellular organelle, ER was the last to be discovered. After years of deliberation, Keith Porter and George Palade in the year 1954,...
The Endoplasmic Reticulum01:43

The Endoplasmic Reticulum

The endoplasmic reticulum or ER makes up for more than half of the membranes in a cell and accounts for 10% of total cell volume. It is also the primary protein and lipid synthesis factory for most cell organelles, such as the Golgi apparatus, lysosomes, secretory vesicles, and the plasma membrane. Despite being the most extensive and functionally complex subcellular organelle, ER was the last to be discovered. After years of deliberation, Keith Porter and George Palade in the year 1954,...
Endoplasmic Reticulum01:39

Endoplasmic Reticulum

Endoplasmic ReticulumThe endoplasmic reticulum (ER) is an extensive network of membranous sacs and tubules in eukaryotic cells, continuous with the outer membrane of the nucleus. This structural continuity integrates nuclear and cytoplasmic processes and facilitates efficient intracellular transport. This allows mRNA to move directly from the nucleus to ribosomes for efficient protein synthesis. As a result, the ER serves as a central site for the synthesis, processing, and distribution of...
Smooth Endoplasmic Reticulum01:21

Smooth Endoplasmic Reticulum

Smooth endoplasmic reticulum or smooth ER is a sub-organelle with specialized functions in animal cells and plant cells. It is often associated with the tubule morphology of the endoplasmic reticulum.
The ER provides optimal conditions for synthesizing steroid hormones and lipids, such as phospholipids and triglycerides. Traditionally, lipid metabolism was considered to be a smooth ER function. However, there is no direct evidence to prove that rough ER is completely excluded from lipid...
Protein Modifications in the RER01:26

Protein Modifications in the RER

Modification of secretory and transmembrane proteins entering the rough ER begins in the ER lumen. These modifications aid in protein folding and stabilize the acquired tertiary structure. Protein modifications in the rough ER co-occur at different stages of protein folding.
Broadly, these modifications can be categorized into four main categories — glycosylation, formation of disulfide bonds, assembly of protein subunits, and specific proteolytic cleavages like removal of signal sequences.
The Early Endosome: Endocytosis of Transferrin01:28

The Early Endosome: Endocytosis of Transferrin

Essential proteins such as insulin or low-density lipoprotein (LDL) and micronutrients such as iron enter a eukaryotic cell through receptor-mediated endocytosis. Subsequently, the early endosomes fuse with the vesicles containing such receptor-ligand complexes and play a vital role in sorting the incoming ligands and receptors. While the ligands are either degraded inside the vesicle or released into the cytosol, their receptors are returned to the plasma membrane for further rounds of...