Function of Transcobalamin II: A B12 Binding Protein in Human Plasma.

Summary1. Transcobalamin II (TC II), a plasma vitamin B12 binding protein, took up cyanocobalamin and hydroxocobalamin when added to plasma in amounts of 1.0 & 25 pg/ml of plasma. 2. It took up B12 when either form of B12 or liver B12 was given by mouth. 3. TC II appears to have a physiological function in plasma transport of B12 when small amounts of B12 are taken into the body in a natural fashion.