Rapid Charcoal Assay for Intrinsic Factor (if), Gastric Juice Unsaturated B12 Binding Capacity, Antibody to If, and Serum Unsaturated B12 Binding Capacity.

Bg CHESTER GorruEB, KAM-SENG LAU, Louis R. \VASSERMAN AND VICTOR HERBERT T HIS COMMUNICATION reports the use of protein-coated charcoal iii rapid assays for: (1) intrinsic factor (IF), (2) unsaturated B12 binding capacity of gastric juice, (3) antibody to IF, and (4) serum unsaturated B12 binding capacity. The assays are based on the finding that charcoal precoated with a large molecule can adsorb only free B12, hut uncoated charcoal can adsorb both free B12 and B12 bound to a large molecule. This concept, derived from our findings and the literature on charcoal1 and on adsorption,2 is schematically depicted in simplified form in figure 1, and supporting evidence presented in figure 2. The background of the present communication is as follows: Using dialysis to separate free from bound B12, Ahels et al.3,4 demonstrated that antibody to IF blocked the ability of IF to bind subsequently added vitamin B12, providing an in vitro assay for autoantibodies to IF and for IF. Ramsey and Herbert5 confirmed the value of this system using a tenfold reduction of ingredients. Four groups of workers had reported that activated charcoal separated free B12 from serum-bound B12; ” Miller1#{176} interpreted his data as indicating increased serum binding of B12 in the presence of IF. Subsequently, based on the observations of Miller, Ardeman and Chanarin1’ reported assays for IF and antibody to IF using charcoal and normal serum. They explained their results on the basis of their belief that charcoal adsorbed both free B12 and the IF-B12 complex, leaving the presumed hut unproved “serum-bound” B12 in the supernatant. They interpreted their data as confirming Miller’s claim of an IF-mediated B12 transfer to serum. Using smaller quantities of serum and gastric juice (0.1 ml.) we were unable to support this claim. Figure 2 shows the effect of increasing quantities of serum in the measurement of the unsaturated B12 binding capacity of 0.1 ml. of normal human gastric juice (NHGJ) using uncoated and pro-