Abstract
At least two major cyanocobalamin-binding sites can be demonstrated in human and animal serum by fractionation on CM-cellulose columns when cyanocobalamin is added in vitro. In normal human serum, Component A, representing 50% of the total binding capacity, is associated with serum albumin and does not bind to CM-cellulose at pH 6. Component B, also representing 50% of the total binding capacity is eluted from the column after the serum globulins at 0.3 M NaCl. Sera from cat, dog, rabbit, horse, cow, pig, sheep, rat, and guinea pig are also resolvable into two major components. The two components in different animal sera are similar but vary with respect to concentration and relative elution pattern. In some animal sera, a third minor cyanocobalamin binding complex (Complex C) is present which is eluted at salt concentrations lower than that necessary for elution of Component B. In chicken serum, Component B is entirely absent. Sera of dogs, rabbits and chickens given oral doses of high specific activity [ 57Co]cyanocobalamin, followed by fractionation on CM-cellulose columns, yield cyanocobalamin binding sites essentially similar to that found for cyanocobalamin added to serum in vitro.
Published Version
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