Characterization of the cobalamins attached to transcobalamin I and transcobalamin II in human plasma.

Insolubilized antibody to transcobalamin I was used to separate transcobalamin I and transcobalamin II. By bioautography of the extracted cobalamins it was shown that transcobalamin II bound more deoxyadenosylcobalamin than did transcobalamin I, and that methylcobalamin accounts for most of the cobalamins attached to transcobalamin I. This finding may indicate that transcobalamin I has a function in the metabolism of methylcobalamin in man.