Studies on the mechanism of cobalamin binding to hog intrinsic factor

Cobalamin binding to hog intrinsic factor has been studied by affinity chromatography, and the cobalt atom of the cobalamin tested was found to be no more than 5 Å from the surface of the protein. A comparative study of the binding of the c carboxylic acid derivative versus the c amide at C₇ of the B pyrrole ring indicates that a change in charge at this position of the corrin ring has little effect on complex formation with intrinsic factor. Furthermore, the coordination sphere in the region of 5,6 dimethyl benzimidazole must be extremely hydrophobic because CN(theta) will not displace this base from the cobalt atom when cobalamin is bound to intrinsic factor.