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  • Title: Separation of cobalamin analogues in human sera binding to intrinsic factor and to R-type vitamin B12 binders.
    Author: Muir M, Chanarin I.
    Journal: Br J Haematol; 1983 Aug; 54(4):613-21. PubMed ID: 6871110.
    Abstract:
    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.
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