COBALAMIN METABOLISM IN CULTURED HUMAN CHORIONIC VILLUS CELLS

Cobalamin (Cbl, vitamin B12) metabolism was analyzed in cultures of hu man chorionic villus (CV) cells obtained at 9-10 weeks of gestation. C V cells were shown to synthesize transcobalamin II (TCII) and to posse ss a high affinity receptor for that molecule. The cells bound and int ernalized radioactive cyanocobalamin (CN[Co-57]Cbl) complexed to TCII. This internalized CN[Co-57]Cbl was found to be converted to both meth ylCbl and adenosylCbl, the two intracellular coenzyme forms of Cbl, an d bound to the two known intracellular Cbl requiring enzymes, methioni ne synthase (MS) and methylmalonyl-CoA mutase. Both enzyme systems wer e found to be functional in the intact cell by demonstrating the incor poration of the radioactive label from both [C-14]CH3-tetrahydrofolate and [C-14] propionate into acid insoluble products. MS activity was a lso detected in lysed cell material. CV cells were shown not to be aux otrophic for methionine since they were able to utilize homocysteine i n place of methionine for cell division. Since CV cells are capable of performing many of the complex events associated with Cbl metabolism, it may be possible to use these cells to diagnose genetic defects of Cbl metabolism. (C) 1993 Wiley-Liss, Inc.