Analysis of ⁵⁷Co-Cbl released from cells. (A left) Gel filtration chromatography of ⁵⁷Co-Cbl in 24 hours of chase medium from cells loaded with ⁵⁷Co-Cbl. The chase of the cells was performed in the absence (■) or presence of 1μM Cbl (○) in the chase medium. (A right) Analysis of the high-molecular-weight complex-form of ⁵⁷Co-Cbl in a high-resolution SMART high-performance liquid chromatography gel filtration system (Superdex 200 column). indicates known position of Cbl in complex with haptocorrin (HC), transcobalamin (TC), as well as free Cbl. (B) Precipitation of ⁵⁷Co-Cbl in 24 hours of efflux medium of the human cells (HeLa cells and fibroblasts) with magnetic beads coated with monoclonal antibodies against human TC or human HC. Precipitation was carried out in chase medium with or without 1μM Cbl added at the initiation of the chase. The values are the means of triplicates ± 1 SD.