• Purity

  >95%, by SDS-PAGE under reducing conditions and visualized by silver stain

• Endotoxin Level

  <0.10 EU per 1 μg of the protein by the LAL method.  

• Activity

  Measured by its binding ability in a functional ELISA. When Recombinant Human CD320/TCblR/8D6A Fc Chimera (Catalog # ) is immobilized at 25 ng/mL (100 μL/well), the concentration of Recombinant Human Transcobalamin II that produces 50% of the optimal binding response is approximately 0.5‑3 ng/mL.

• Source

  Chinese Hamster Ovary cell line, CHO-derived Glu19-Trp427 with a C-terminal 6-His tag

• Accession #

• N-terminal Sequence    
  Analysis

  Glu19 & Cys21

• Predicted Molecular Mass

  46.4 kDa

• SDS-PAGE

  41-43 kDa, reducing conditions

Background: Transcobalamin II

Transcobalamin II (TCII) is an approximately 44 kDa protein that serves as a circulating carrier for cobalt‑containing Vitamin B  ₁₂ (also known as Cobalamin, or Cbl). Vitamin B  ₁₂ plays an important role as a coenzyme during amino acid and nucleotide metabolism. Chronic deficiency of Vitamin B  ₁₂ intake, absorption, or transport leads to serious health risks including megaloblastic anemia and neurologic symptoms. Prior to its interaction with TCII, dietary Vitamin B  ₁₂ is bound by salivary Transcobalamin I (Haptocorrin) which shields it from the acidic environment of the stomach. Vitamin B  ₁₂ is subsequently transferred to Transcobalamin III (also known by its traditional name Intrinsic Factor, or IF) following the proteolytic degradation of Transcobalamin I in the small intestine. Transcobalamin III- Vitamin B  ₁₂ complexes are internalized into intestinal epithelial cells (IEC) by Cubam, which is a receptor complex containing the proteins Cubilin and Amnionless (1). IF is degraded within the IEC, while free Vitamin B  ₁₂ is transcytosed and actively pumped across the basolateral membrane by the efflux transporter MRP1 (2, 3). Here, Vitamin B  ₁₂ is picked up by TCII, which is secreted by vascular endothelial cells into the interstitial space between IEC (4). TCII binds to free Vitamin B  ₁₂ with high affinity and is critical for the passage of Vitamin B  ₁₂ into the blood stream (5, 6). Circulating TCII- Vitamin B  ₁₂ complexes are bound and internalized by the widely expressed TCII Receptor, also known as CD320 and 8D6A (7). A soluble form of CD320 circulates in the serum (8). TCII is then degraded intracellularly, and Vitamin B  ₁₂ can function as a cofactor for methionine synthase and methylmalonyl-CoA mutase (1). In the kidney, TCII- Vitamin B  ₁₂ complexes are filtered and reabsorbed through interactions with Megalin on proximal tubule epithelial cells (9). Megalin also directly interacts with CD320 in these cells (10). CD320 is additionally expressed on placental membranes for Vitamin B  ₁₂ delivery to the developing fetus (11). Mature human TCII shares 74% amino acid (aa) sequence identity with mouse and rat TCII (12). Alternative splicing of human TCII generates a short isoform with a 27 aa internal deletion.

• References:

1. Nielsen, M.J. et al. (2012) Nat. Rev. Gastroenterol. Hepatol. 9:345.

2. Dan, N. and D.F. Cutler (1994) J. Biol. Chem. 269:18849.

3. Beedholm-Ebsen, R. et al. (2010) Blood 115:1632.

4. Quadros, E.V. et al. (1999) Am. J. Physiol. 277:G161.

5. Hall, C.A. (1975) J. Clin. Invest. 56:1125.

6. Bose, S. et al. (1997) J. Biol. Chem. 272:3538.

7. Quadros, E.V. et al. (2009) Blood 113:186.

8. Arendt, J.F. et al. (2011) Clin. Chem. Lab. Med. 50:515.

9. Moestrup, S.K. et al. (1996) Proc. Natl. Acad. Sci. USA 93:8612.

10. Yammani, R.R. et al. (2003) J. Membr. Biol. 193:57.

11. Friedman, P.A. et al. (1977) J. Clin. Invest. 59:51.

12. Platica, O. et al. (1991) J. Biol. Chem. 266:7860.

• Entrez Gene IDs:

  6948 (Human); 21452 (Mouse); 64365 (Rat)

• Alternate Names:

  D22S676; D22S750; macrocytic anemia; TC; TC-2; TC2II; TCII; TCN2; Transcobalamin II; transcobalamin II; macrocytic anemia; transcobalamin IITC II; transcobalamin-2; Vitamin B12-binding Protein 2