Abstract
A purified hog intestinal receptor for intrinsic factor-vitamin B_<12> complex was labeled with ^<125>I. The labeled receptor had an apparent molecular weight of 460,000 on gel filtration through Sepharose 6B column and an isoelectric point of 4.48. It reacted with the anti-serum against the receptor to yield a macromolecular complex. When the receptor was assayed in a double anti-body radioimmunoassay using the ^<125>I-labeled receptor, good standard curves were obtained and non-specific, binding was less than 1.2%. A good agreement was obtained between receptor activities assayed by gel filtration and receptor contents measured by the present radioimmunoassay method by studying several receptor preparations with different specific activities. The method is simple to perform, precise and sensitive and makes it possible to assay the receptor in large batches.
