The endoplasmic reticulum (endoplasmic meaning "within the cytoplasm," reticulum meaning "little net" in Latin) or ER is an organelle found in all eukaryotic cells that is an interconnected network of tubules, vesicles and cisternae that is responsible for several specialized functions: Protein translation, folding, and transport of proteins to be used in the cell membrane (e.g., transmembrane receptors and other integral membrane proteins), or to be secreted (exocytosed) from the cell (e.g., digestive enzymes); sequestration of calcium; and production and storage of glycogen, steroids, and other macromolecules. The endoplasmic reticulum is part of the endomembrane system. The basic structure and composition of the ER membrane is similar to the plasma membrane.

4B4

• may serve as a specific marker for the sarcoplasmic/endoplasmic reticulum Ca2+ pump system in various cells, and can provide quantitative information about the loss of active Ca2+ pump proteins under pathological conditions. PMID: 2543829

Calnexin

• a membrane-bound chaperone of the endoplasmic reticulum. PMID: 8203019
• calnexin, which is itself retained within the endoplasmic reticulum, is normally expressed on the surface of various cells such as mastocytoma cells, murine splenocytes, fibroblast cells, and human HeLa cells. PMID: 10956670

Calreticulin

• Calreticulin and calnexin are Ca2+-binding proteins with chaperone activity in the endoplasmic reticulum. PMID: 11726513

Cytochrome P450 (CYP2E1)

• an endoplasmic reticulum marker. PMID: 1918014

Disulfide Isomerase

• classical ER resident. PMID: 15281078

Estrone Sulfate Sulfohydrolase

• a putative endoplasmic reticulum marker. PMID: 219149

CDP-Choline-Diacylglycerol Cholinephosphotransferase.

• a putative endoplasmic reticulum marker. PMID: 219149

Epoxide Hydrolase

• a marker for the smooth endoplasmic reticulum in rat liver. PMID: 4065094

ERp27

• a new non-catalytic endoplasmic reticulum-located human protein disulfide isomerase family member, interacts with ERp57. PMID: 16940051

ERp29

• a recently discovered resident of the endoplasmic reticulum (ER) that is abundant in brain and most other mammalian tissues. PMID: 15281078

ERp57

• a member of the protein disulfide isomerase (PDI) family that is located in the endoplasmic reticulum (ER) and characterized by its specificity for glycoproteins. PMID: 14871899

ERp72

• a resident protein of the endoplasmic reticulum (ER) is both a stress protein and a member of the protein disulfide isomerase family of proteins. PMID: 8216852
• an abundant luminal endoplasmic reticulum protein, contains three copies of the active site sequences of protein disulfide isomerase. PMID: 2295602

Glucose-6-Phosphatase (G-6-Pase)

• an endoplasmic reticulum marker. PMID: 8652599
• localized consistently within the lumen of all endoplasmic reticulum, nuclear space and subsurface cisternae, and frequently in the concave saccules of the Golgi apparatus. PMID: 2552716
• a cytochemical marker of endoplasmic reticulum in human leukocytes and platelets. PMID: 6319482

Glucosidase II

• a protein of the endoplasmic reticulum with high mannose oligosaccharide chains and a rapid turnover. PMID: 3546312
• an asparagine-linked oligosaccharide processing enzyme, is a resident glycoprotein of the endoplasmic reticulum. In kidney tubular cells, in contrast to previous findings on hepatocytes, we found by light and electron microscopy immunoreactivity for glucosidase II predominantly in post-Golgi apparatus structures. PMID: 2404989

GRP78/BiP

• the major chaperone of the endoplasmic reticulum (ER) lumen. PMID: 9388233
• lumenal stress protein of the endoplasmic reticulum (ER) that interacts with polypeptide folding intermediates transiting the secretory compartment. PMID: 9020152
• a constitutively-expressed resident protein of the endoplasmic reticulum (ER) of all eucaryotic cells, and belongs to the highly conserved hsp70 protein family. PMID: 7988659
• BiP/GRP78 is a member of the HSP70 family involved in the folding and assembly of proteins in the endoplasmic reticulum. PMID: 8020977
• induction of GRP78 is a marker for ER stress. GRP78, also referred to as BiP, is a central regulator for ER stress due to its role as a major ER chaperone with anti-apoptotic properties as well as its ability to control the activation of transmembrane ER stress sensors (IRE1, PERK, and ATF6) through a binding-release mechanism. PMID: 15804610
• BiP is selectively retained in the cisternae of the ER and is not free to enter Golgi-directed transport vesicles. PMID: 2685110

GRP94

• a glycoprotein in the endoplasmic reticulum (ER). PMID: 9009140
• endoplasmic reticulum stress protein. PMID: 1400441

ERp99

• an abundant, conserved transmembrane glycoprotein of the endoplasmic reticulum membrane. PMID: 3036833

Heme oxygenase-1

• a cytoprotective protein that catalyzes the degradation of heme to biliverdin, iron, and carbon monoxide (CO). Endoplasmic reticulum (ER) stress induced by a variety of experimental agents stimulated a time- and concentration-dependent increase in HO-1 mRNA and protein in vascular smooth muscle cells (SMC). PMID: 15546873

HSP27

• cytosolic resident heat shock protein located in the endoplasmic reticulum (ER). PMID: 16884889
• Endoplasmic reticulum stress induces the phosphorylation of small heat shock protein, Hsp27. PMID: 15864808

JPDI (J-domain-containing protein disulfide isomerase-like protein)

• a novel endoplasmic reticulum-resident protein containing both a BiP-interacting J-domain and thioredoxin-like motifs. PMID: 12446677

Membrin

• an ER-Golgi SNARE protein. PMID: 15781476
• a protein implicated earlier in ER-to-Golgi transport. PMID: 9349823

NADPH cytochrome c (cyt c) reductase and glucose-6-phosphatase

• two enzymes thought to be restricted to the endoplasmic reticulum (ER) and widely used as ER markers. PMID: 214450

PDI (Protein Disulphide Isomerase)

• one such ER resident protein that has been previously shown to interact with proteins during their folding and assembly pathways. PMID: 11509234

Rbet1

• homologous to yeast Bet1p is primarily associated with the pre-Golgi intermediate compartment and is involved in vesicular transport from the endoplasmic reticulum to the Golgi apparatus. PMID: 9382863

Tapasin (tpn)

• an essential component of the MHC class I (MHC I) loading complex, has a canonical double lysine motif acting as a retrieval signal, which mediates retrograde transport of escaped endoplasmic reticulum (ER) proteins from the Golgi back to the ER. PMID: 16751394
• a subunit of the transporter associated with antigen processing (TAP). PMID: 11884415
• is retained in the endoplasmic reticulum by dynamic clustering and exclusion from endoplasmic reticulum exit sites. PMID: 11823478

TbRab2p

• localised primarily to the endoplasmic reticulum (ER) and colocalises with BiP in wild-type trypanosomes, is a marker for the endoplasmic reticulum of Trypanosoma brucei, localises to the ERGIC in mammalian cells. PMID: 9858468

UGGT

• gamma -glutamyltransferase and its isoform mediate an endoplasmic reticulum stress response. PMID: 11116135
• Gamma-glutamyltransferase induction was maximal 24 h after PB treatment in both the rough endoplasmic reticulum and the plasma membranes after a single dose of phenobarbital (PB) (75 mg kg-1 body weight). PMID: 2886233

Other ER Markers

• Two sensitive, convenient, and widely applicable assays for marker enzyme activities specific to endoplasmic reticulum. PMID: 2840001
• Anti-liver-kidney microsome antibody is a marker for the rat hepatocyte endoplasmic reticulum. PMID: 3552922
• Peroxidase, a marker enzyme for granular endoplasmic reticulum in thyroid gland (proceedings). PMID: 79388
• Preneoplastic antigen as a marker for endoplasmic reticulum of putative premalignant hepatocytes during liver carcinogenesis. PMID: 193631