Complexing of Transcobalamin 2 and Apparent Combination With Heparin

⁵⁷Co cyanocobalamin mixed with serum filters through sephadex G-150 in two fractions, corresponding to apparent molecular weights of about 120,000 and 36,000, respectively. Much of the native B₁₂ also filters in these fractions, but some is excluded from the gel, and a large fraction filters in the position of free B₁₂. When heparin is mixed with serum or plasma, most of the B₁₂ filters with the 120,000 fraction. When EDTA is mixed with serum or plasma not containing heparin, less ⁵⁷CoB₁₂ filters in the 120,000 fraction, and more filters in the 36,000 fraction. The 120,000 and 36,000 fractions cannot therefore be assumed to correspond precisely with transcobalamin 1 and 2, respectively.

It is suggested that heparin binds transcobalamin 2 and that EDTA dissociates either TC2 complexes or some of the TC1.