Unsaturated and cobalamin saturated transcobalamin I and II in normal human plasma.

Insolubilized antibody against human transcobalamin I has been used as a specific and precise tool for the separation of transcobalamin I (and III) from transcobalamin II. Range and mean (in parentheses) for the unsaturated binding capacity for twenty samples are 40-190 (90) pmol/l and 220-1170 (560) pmol/l for transcobalamin I (and III) and transcobalamin II, respectively. The similar figures for the cobalamin saturated transcobalamins are 200-549 (320) pmol/l and 75-475 (160 pmol/l. On analyses of the cobalamins attached to each of the transcobalamins, it is shown that methylcobalamin accounts for most of the cobalamins attached to transcobalamin I whereas transcobalamin II carries most of the 5'-deoxyadenosylcobalamin.