Radioiodination of human intrinsic factor

Iain L. Mackenzie; Robert M. Donaldson; Robert F. Schilling

doi:10.1172/JCI106009

Radioiodination of human intrinsic factor

Iain L. Mackenzie, Robert M. Donaldson Jr., and Robert F. Schilling

Published March 1, 1969 - More info

View PDF

Abstract

Human intrinsic factor (IF) saturated with ⁶⁰Co-labeled cyanocobalamin (⁶⁰CoB₁₂) was purified and then iodinated with ¹²⁵I to yield ¹²⁵I-labeled IF-⁶⁰CoB₁₂ preparations of high specific activity. Sephadex G200 and DEAE-cellulose chromatography of the iodinated IF-⁶⁰CoB₁₂ complex showed coincidence of the major ¹²⁵I and the ⁶⁰Co radioactivity peaks. During starch-gel electrophoresis ⁶⁰Co radioactivity from noniodinated and iodinated complexes migrated to the same extent while ¹²⁵I radioactivity from the iodinated complex migrated slightly further anodally than did the ⁶⁰Co radioactivity. After the iodinated complex was mixed with antibody to the IF-B₁₂ complex (antibody II) the ¹²⁵I and ⁶⁰Co radioactivity were: (a) precipitated in similar amounts by antiglobulin serum. (b) eluted coincidentally in the 19S region on Sephadex G200, and (c) excluded to the same extent from starch gel during electrophoresis. After equilibrium exchange of IF “blocking” antibody (antibody I) for ⁶⁰Co-vitamin B₁₂ on ¹²⁵I-labeled IF. ¹²⁵I radioactivity from the IF-antibody I complex: (a) was precipitated by antiglobulin serum, (b) was eluated in the 19S region on Sephadex G200 gel filtration, and (c) migrated slowly towards the anode on starch-gel electrophoresis. Urinary excretion of ⁶⁰Co radioactivity in pernicious anemia patients after oral administration of ⁶⁰Co-vitamin B₁₂ bound to freshly prepared ¹²⁵I-labeled IF was similar to that obtained with noniodinated intrinsic factor.

These results show that iodination of IF-⁶⁰CoB₁₂ complex does not markedly alter the chromatographic, electrophoretic, antigenic, or absorption-promoting properties of IF.