title: The dynamics of cobalamin utilization in L-1210 mouse leukemia cells: a model of cellular cobalamin metabolism.
abstract: The uptake and metabolism of cobalamin (Cbl) has been studied in L-1210 murine leukemia cells propagating in vitro. Extracellular Cbl (protein bound and free) and intracellular Cbl (protein bound and free) were determined after culturing L-1210 cells in the presence of [57Co]cyanocobalamin (CN-Cbl) bound to transcobalamin II (transcobalamin, TC). The intracellular pool of free [57Co]Cbl increased during the first 24 h of culture and a substantial fraction of this free pool was effluxed from the cell to the medium. Upon depletion of extracellular TC-[57Co]CN-Cbl, the intracellular concentration of free Cbl decreased as did the efflux of Cbl to the medium. Internalized [57Co]CN-Cbl was converted to hydroxocobalamin (OH-Cbl), methylcobalamin (Me-Cbl) and 5'-deoxyadenosylcobalamin. These Cbl forms were found in both soluble (cytoplasmic) and insoluble (membrane) fractions. Intracellular protein-bound [57Co]Cbl fractionated with methionine synthase (MS) and methylmalonyl-CoA mutase (MU) activity. The major form of Cbl associated with the two enzymes was OH-Cbl. Cells propagated in medium containing N5-methyltetrahydrofolate and homocysteine showed a substantial increase in MS activity which paralleled the increase in the intracellular concentration of Me-Cbl and the Cbl bound to the enzyme.
authors.affiliation: Division of Hematology/Oncology V.A. Medical Center, Brooklyn, NY 11209, USA.
authors.forename: E V
authors.initials: EV
authors.lastname: Quadros
authors.forename: D W
authors.initials: DW
authors.lastname: Jacobsen
mesh_terms: D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase / Q000378:metabolism; D000818:Animals; D003037:Cobalt Radioisotopes; D003038:Cobamides / Q000378:metabolism; D017077:Culture Media, Conditioned; D006879:Hydroxocobalamin / Q000378:metabolism; D007939:Leukemia L1210 / Q000378:metabolism*; D008765:Methylmalonyl-CoA Mutase / Q000378:metabolism; D051379:Mice; D014155:Transcobalamins / Q000378:metabolism; D014805:Vitamin B 12 / Q000031:analogs & derivatives / Q000378:metabolism*
chemical_list: D003037:Cobalt Radioisotopes; D003038:Cobamides; D017077:Culture Media, Conditioned; D014155:Transcobalamins; C019476:mecobalamin; D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase; D008765:Methylmalonyl-CoA Mutase; C000913:cobamamide; D014805:Vitamin B 12; D006879:Hydroxocobalamin