Folate-dependent enzymes in cultured Chinese hamster ovary cells: impaired mitochondrial serine hydroxymethyltransferase activity in two additional glycine-auxotroph complementation classes
Two glycine-requiring Chinese hamster ovary (CHO) auxotrophs (GLYB and AUXB2) representative of the Gly/sup -/ mutant classes B and C are shown to have defects in folate metabolism. These defects result in 10-fold lower rates of whole cell L-(U-/sup 14/C)serine-to-(/sup 14/C)glycine conversion relative to the parental CHO lines (2 vs 20 nmol/h/10/sup 6/ cells). This restriction in serine hydroxymethyltransferase (SHMT) activity is localized in the mitochondria. Intact mitochondria from GLYB and AUXB2 convert labeled serine to glycine at 1-4% the rate and with only 1-3% of the total capacity of parental CHO mitochondria. Yet, GLYB and AUXB2 contain parental cell amounts of cytosolic and mitochondrial SHMT, the latter displaying normal substrate K/sub m/ values. The whole cell and mitochondrial impairments in glycine formation are corrected in GLYB (but not AUXB2) by a prior growth with 100 ..mu..M dl-folinate. They are also partially restored in spontaneous or chemically induced Gly/sup +/ revertants of GLYB and AUXB2. Subcellular fractionation experiments suggest that a low content (one-fifth parental) of mitochondrial folylpolyglutamates contributes to the auxotrophy of GLYB. These studies demonstrate that mitochondrial SHMT is potentially functional in the Gly/sup -/ mutant classes B (GLYB) and C (AUXB2). The impaired SHMT activity in vivo and in isolated mitochondria may result from a deficiency in mitochondrial recycling of 5,10-methylenetetrahydrofolate back to tetrahydrofolate.
- Research Organization:
- Univ. of California, Berkeley
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 5217748
- Journal Information:
- Arch. Biochem. Biophys.; (United States), Vol. 217:2
- Country of Publication:
- United States
- Language:
- English
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FOLIC ACID
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TRANSFERASES
BIOCHEMISTRY
CARBON 14 COMPOUNDS
FIBROBLASTS
GLYCINE
HAMSTERS
MITOCHONDRIA
MUTANTS
SERINE
AMINO ACIDS
ANIMAL CELLS
ANIMALS
AROMATICS
AZAARENES
CARBOXYLIC ACIDS
CELL CONSTITUENTS
CHEMISTRY
CONNECTIVE TISSUE CELLS
DRUGS
ENZYMES
HEMATINICS
HEMATOLOGIC AGENTS
HETEROCYCLIC COMPOUNDS
HYDROXY ACIDS
HYDROXY COMPOUNDS
LABELLED COMPOUNDS
MAMMALS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANOIDS
PTERIDINES
RODENTS
SOMATIC CELLS
VERTEBRATES
VITAMIN B GROUP
VITAMINS
550200* - Biochemistry
550300 - Cytology
550400 - Genetics