Development of a Possible in vitro Assay for Intrinsic Factor. ∗ †

Abstract

Summary

When rat liver slices are incubated in hog intrinsic factor concentrate (HIFC) and Co⁶⁰-B₁₂ simultaneously, there is an optimal concentration of HIFC producing maximal Co⁶⁰-B₁₂ uptake by the liver slices. Any deviation from this optimal level results in a decreased enhancement of Co⁶⁰-B₁₂ uptake. Slices incubated in high concentration of HIFC, washed, and then incubated in Co⁶⁰-B₁₂ take up much more Co⁶⁰-B₁₂ than slices incubated in these materials together. From these facts the hypothesis was derived that receptors for intrinsic factor may exist on rat liver slices, and that these receptors can “take up”either free intrinsic factor or intrinsic factor to which Co⁶⁰-B₁₂ is attached. A possible in vitro assay for intrinsic factor is presented, based on sequential incubation of rat liver slices in intrinsic factor-containing buffer and then in Co⁶⁰-B₁₂.