Endoplasmic reticulum: A metabolic compartment

Abstract 

Several biochemical reactions and processes of cell biology are compartmentalized in the endoplasmic reticulum (ER). The view that the ER membrane is basically a scaffold for ER proteins, which is permeable to small molecules, is inconsistent with recent findings. The luminal micro-environment is characteristically different from the cytosol; its protein and glutathione thiols are remarkably more oxidized, and it contains a separate pyridine nucleotide pool. The substrate specificity and activity of certain luminal enzymes are dependent on selective transport of possible substrates and co-factors from the cytosol. Abundant biochemical, pharmacological, clinical and genetic data indicate that the barrier function of the lipid bilayer and specific transport activities in the membrane make the ER a separate metabolic compartment.

Abbreviations: ER, endoplasmic reticulum, GSH, glutathione, GSSG, glutathione disulfide, GSD 1, glycogen storage disease type 1, CRD, cortisone reductase deficiency, G6P, glucose-6-phosphate, G6Pase, glucose-6-phosphatase, G6PT, glucose-6-phosphate transporter, H6PDH, hexose-6-phosphate dehydrogenase, 11βHSDH1, 11β-hydroxysteroid dehydrogenase type 1, MHC, major histocompatibility complex, RER, rough endoplasmic reticulum, TAP, transporter associated with antigen processing, UGA, UDP-glucuronic acid, UGT, UDP-glucuronosyltransferase

Keywords: Endoplasmic reticulum, Membrane, Permeability, Transport, Compartment, Barrier, Latency, Specificity, Lumen