Gastric parietal cells secrete cobalamin binding intrinsic factor (CBLIF, aka gastric intrinsic factor GIF) which binds tightly to free cobalamins (RCbl) released from transcobalamin (TCN1, haptocorrin) in the proximal intestine (Matthews et al. 2007). RCbl must bind to CBLIF to be absorbed from the small intestine.
Gordon, MM, Mathews, FS, Ealick, SE, Alpers, DH, Chen, Z, Rajashankar, KR, Sukumar, N
cargo receptor ligand activity of CBLIF [extracellular region]
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