Separation of cobalamin analogues in human sera binding to intrinsic factor and to R-type vitamin B12 binders.
Intrinsic factor (IF) and cobalamin-R-binding protein (R-binder) linked to polyacrylamide beads were used to absorb cobalamins from solutions and serum extracts. Both binding agents were equally effective in removing [57Co]B12 from aqueous solution. IF was more effective than R-binder in removing [57Co]B12 added to a serum extract. All endogenous cobalamins detectable in serum by saturation analysis assay were removed by absorption onto R-binder. Absorption with IF removed microbiologically-active cobalamins but left behind analogues assayable with an R-binder. However, when absorption with IF was continued the concentration of R-binding cobalamins steadily declined indicating that IF bound both types of cobalamins through the binding was less avid for the microbiologically-inactive analogues than for microbiologically-active cobalamins. Finally, the R-binding analogues in serum were carried on transcobalamin I and none was detectable on transcobalamin II. The absorption studies establish the presence of two types of cobalamins one binding preferentially to IF and the other preferentially to R-binder. Only the former is detected by microbiological assay.
D000042:Absorption; D001667:Binding, Competitive; D001681:Biological Assay; D001798:Blood Proteins / Q000378:metabolism*; D003956:Dialysis; D006801:Humans; D007437:Intrinsic Factor / Q000378:metabolism*; D008722:Methods; D014155:Transcobalamins / Q000378:metabolism*; D014805:Vitamin B 12 / Q000031:analogs & derivatives / Q000097:blood*
D001798:Blood Proteins; D014155:Transcobalamins; D007437:Intrinsic Factor; D014805:Vitamin B 12