Recombinant Human Transcobalamin II Catalog Number: 7895-TC

Recombinant Human Transcobalamin II Catalog Number: 7895-TC

DESCRIPTION Source Chinese Hamster Ovary cell line, CHO­derived Glu19­Trp427 with a C­terminal 6­His tag Accession # P20062

N­terminal Sequence Glu19 & Cys21 Analysis Predicted Molecular 46.4 kDa Mass

SPECIFICATIONS SDS­PAGE 41­43 kDa, reducing conditions

Activity Measured by its binding ability in a functional ELISA. When Recombinant Human CD320/TCblR/8D6A Fc Chimera (Catalog # 1557­CD) 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 0.5­3 ng/mL.

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

Purity >95%, by SDS­PAGE under reducing conditions and visualized by silver stain. Formulation Lyophilized from a 0.2 μm filtered solution in PBS. See Certificate of Analysis for details.

PREPARATION AND STORAGE Reconstitution Reconstitute at 200 μg/mL in PBS.

Shipping The product is shipped at ambient temperature. Upon receipt, store it immediately at the temperature recommended below. Stability & Storage Use a manual defrost freezer and avoid repeated freeze­thaw cycles. l 12 months from date of receipt, ­20 to ­70 °C as supplied. l 1 month, 2 to 8 °C under sterile conditions after reconstitution. l 3 months, ­20 to ­70 °C under sterile conditions after reconstitution.

BACKGROUND

Transcobalamin II (TCII) is an approximately 44 kDa protein that serves as a circulating carrier for cobalt­containing Vitamin B12 (also known as Cobalamin, or Cbl). Vitamin B12 plays an important role as a coenzyme during amino acid and nucleotide metabolism. Chronic deficiency of Vitamin B12 intake, absorption, or transport leads to serious health risks including megaloblastic anemia and neurologic symptoms. Prior to its interaction with TCII, dietary Vitamin B12 is bound by salivary Transcobalamin I (Haptocorrin) which shields it from the acidic environment of the stomach. Vitamin B12 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 B12 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 B12 is transcytosed and actively pumped across the basolateral membrane by the efflux transporter MRP1 (2, 3). Here, Vitamin B12 is picked up by TCII, which is secreted by vascular endothelial cells into the interstitial space between IEC (4). TCII binds to free Vitamin B12 with high affinity and is critical for the passage of Vitamin B12 into the blood stream (5, 6). Circulating TCII­ Vitamin B12 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 B12 can function as a cofactor for methionine synthase and methylmalonyl­CoA mutase (1). In the kidney, TCII­ Vitamin B12 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 B12 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. Beedholm­Ebsen, 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.

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