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

Area of Science:

• Biochemistry
• Molecular Biology
• Protein Chemistry

Background:

• Human intrinsic factor (IF) is essential for vitamin B12 absorption in the ileum.
• Understanding the structure of IF is key to elucidating its function in cobalamin (vitamin B12) binding and transport.
• Previous studies have focused on the overall structure and function, but detailed sequence information has been limited.

Purpose of the Study:

• To determine a significant portion of the amino acid sequence of human intrinsic factor.
• To identify specific regions or residues involved in cobalamin binding.
• To contribute to a deeper understanding of the molecular basis of vitamin B12 absorption.

Main Methods:

• Purification of human intrinsic factor using labile ligand affinity chromatography.
• Chemical cleavage of purified intrinsic factor using cyanogen bromide.
• Fractionation of cleaved fragments via gel filtration chromatography.
• Purification and sequencing of individual peptide fragments.

Main Results:

• Successfully sequenced a total of eighty-four amino acid residues, representing approximately one-third of the human intrinsic factor sequence.
• Identified four purified fragments from the cyanogen bromide cleavage.
• Discovered a specific tyrosine residue within one fragment that is uniquely labeled upon iodination of intrinsic factor when it is devoid of cobalamin, suggesting its proximity or involvement in the cobalamin binding site.

Conclusions:

• The determined amino acid sequence provides valuable structural information about human intrinsic factor.
• The identified tyrosine residue is a key finding, potentially located within or near the cobalamin binding domain.
• This research lays the groundwork for further structural and functional studies of intrinsic factor and its role in vitamin B12 absorption.