A comparison of the properties of chicken serum with other vitamin B12 binding proteins used in radioisotope dilution methods for measuring serum vitamin B12 concentrations.

Abstract

Summary. The effects of pH, ionic strength, and vitamin B12 concentration on the vitamin B12 ‐binding capacities of chicken serum, normal human serum, chronic myelogenous leukaemia serum, and hog intrinsic factor concentrates are compared. The influence of pH on B12‐binding capacity was shown to be greatest at low pH and that of ionic strength was most evident below 0.1 ionic strength, particularly at acidic pH. The effect of B12 concentration on B12‐binding capacity was shown to vary with different binders, the pH of binding, and the time of incubation.It was possible to select conditions for carrying out the binding of B12 to chicken serum so that the amount of B12 bound was virtually unaffected by the kind of variations in pH, ionic strength, or concentration of B12 that could occur in a radioisotope dilution assay of serum vitamin B12. Under these conditions it was further demonstrated that the binding was unaffected by the presence of denatured human serum. In addition chicken serum had a very great binding capacity and affinity for B12, was very stable on storage and was compatible with the use of protein‐coated charcoal.Some conclusions on the optimal use of B12‐binding protein in the radioisotope dilution assay of serum vitamin B12 are made and the high potentiality of chicken serum in such a system is suggested.