The mechanism of cobalamin binding to hog intrinsic factor

Circular dichroism studies on the methylcobalamin-intrinsic factor complex, together with studies on the carbethoxylation of histidine residues in this complex, indicate that 5,6 dimethylbenzimidazole is probably displaced by a histidine residue of intrinsic factor which coordinates to the cobalt atom at the sixth coordination site. In addition, the stability of the CoC σ bond for methylcobalamin bound to intrinsic factor is identical to that stability measured for the free methyl-cobinamide-histidine complex, but considerably different from the stability of this σ bond in free methylcobalamin.