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Identification and characterization of human mitochondrial methenyltetrahydrofolate synthetase activity
R Bertrand1, M Beauchemin, A Dayan
1Centre de Recherche Louis-Charles Simard, Institut du Cancer de Montréal, Canada.
Abstract:
We present evidence for the presence of the folate metabolism enzyme methenyltetrahydrofolate synthetase (MTHFS) in mitochondria. MTHFS activity was identified in the matrix of mitochondria purified from human liver biopsies. Mitochondrial and cytoplasmic MTHFS specific activities are similar, 85% of the total cellular MTHFS activity is in the cytoplasm and both native enzymes have similar molecular weights (approximately 25 kDa). Studies using purified mitochondrial MTHFS from CA46 human Burkitt lymphoma cells reveal that mitochondrial MTHFS behaves kinetically like the cytoplasmic enzyme with Km values of 4.7, 0.8 and 22 microM respectively for (6R,S)-5-formyltetrahydrofolate monoglutamate, (6S)-5-formyltetrahydrofolate pentaglutamate and ATP. This finding adds to previous observations that various folate-dependent enzymes reside in the mitochondria of eucaryotic cells. Intracellular tetrahydrofolate metabolism is highly compartmentalized and mitochondrial MTHFS activity is necessary for the entry of mitochondrial 5-formyltetrahydrofolate into the mitochondrial folate pool.
Insights
The enzyme methenyltetrahydrofolate synthetase (MTHFS) is present in human mitochondria, playing a key role in folate metabolism. This mitochondrial MTHFS is crucial for folate processing within the cell's energy-producing organelles.
Area of Science:
- Biochemistry
- Cell Biology
- Molecular Biology
Background:
- Folate metabolism is essential for cellular functions.
- Intracellular folate metabolism is known to be compartmentalized.
- Previous studies suggest various folate-dependent enzymes are located in mitochondria.
Purpose of the Study:
- To investigate the presence and function of methenyltetrahydrofolate synthetase (MTHFS) in mitochondria.
- To characterize the kinetic properties of mitochondrial MTHFS.
- To understand the role of mitochondrial MTHFS in intracellular folate metabolism.
Main Methods:
- Purification of mitochondria from human liver biopsies and CA46 human Burkitt lymphoma cells.
- Assay of MTHFS activity in isolated mitochondrial matrix.
- Kinetic analysis of purified mitochondrial MTHFS using different folate substrates and ATP.
Main Results:
- MTHFS activity was detected in the matrix of human liver mitochondria.
- Mitochondrial and cytoplasmic MTHFS exhibit similar specific activities and molecular weights (~25 kDa).
- Kinetic studies showed mitochondrial MTHFS behaves similarly to the cytoplasmic enzyme, with specific Km values for substrates.
Conclusions:
- MTHFS is present in the mitochondria of human cells.
- Mitochondrial MTHFS activity is vital for incorporating 5-formyltetrahydrofolate into the mitochondrial folate pool.
- This finding contributes to the understanding of compartmentalized folate metabolism in eukaryotic cells.