Primary structure of human intrinsic factor: progress report on cyanogen bromide fragmentation.

Human intrinsic factor purified by labile ligand affinity chromatography was cleaved with cyanogen bromide and fractionated by gel filtration. Four of the fragments were purified and sequenced to a total of eighty-four amino acid residues. Including the N-terminal amino acids this amounts to one third of the total amino acid sequence of human intrinsic factor. One of the fragments contained a tyrosine labelled only on iodination of intrinsic factor devoid of cobalamin.