REGULATION OF FOLATE AND ONE-CARBON METABOLISM IN MAMMALIAN-CELLS .3.ROLE OF MITOCHONDRIAL FOLYLPOLY-GAMMA-GLUTAMATE SYNTHETASE

Wild-type Chinese hamster ovary (CHO) cells and CHO cell transfectants expressing human folylpoly-gamma-glutamate synthetase (FPGS) activity contain mitochondrial FPGS activity of higher specific activity than the cytosolic isozyme. Expression of mitochondrial FPGS activity is re quired for folate accumulation by mitochondria. The mitochondrial fola te pool in CHO cells is not in equilibrium with the cytosolic pool and contains folylpolyglutamates of longer glutamate chain length than cy tosolic folates. The inability of AUX-coli, a CHO cell expressing high levels of Escherichia coli FPGS activity and containing pteroyltriglu tamate, to support glycine synthesis is due to a lack of mitochondrial FPGS activity. AUX-coli cells lack mitochondrial folate despite conta ining high levels of cytosolic folate.