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Uptake of cobalamin by Euglena mitochondria
F Watanabe1, Y Tamura, E Stupperich
1Laboratory of Nutrition and Food Science, Hagoromo-gakuen College, Osaka.
Journal of Biochemistry
|December 1, 1993
Summary
Euglena mitochondria actively transport cobalamin (vitamin B12) via an ATP-dependent process. This uptake is highly specific, requiring the complete vitamin B12 molecule and involving soluble mitochondrial proteins.
Area of Science:
- Mitochondrial Biology
- Nutrient Transport
- Biochemistry
Background:
- Cobalamin (vitamin B12) is essential for various metabolic processes.
- Mitochondria play a crucial role in cellular energy metabolism and nutrient processing.
- Understanding nutrient uptake mechanisms in organelles is vital for cell biology.
Purpose of the Study:
- To elucidate the mechanism and specificity of cobalamin uptake by Euglena mitochondria.
- To identify the cellular components involved in mitochondrial cobalamin transport and binding.
Main Methods:
- Investigated cobalamin uptake kinetics in Euglena mitochondria.
- Utilized cobalamin analogues to assess structural requirements for uptake.
- Analyzed mitochondrial fractions to identify cobalamin-binding proteins.
Main Results:
- Cobalamin uptake is a biphasic process: energy-independent binding followed by energy-dependent transport requiring matrix ATP.
- Uptake is highly specific for intact cobalamin, with a dissociation constant of 0.45 nM for membrane binding.
- Three soluble mitochondrial proteins (MW >700,000, 160,000, and 35,000) bind the internalized cobalamin.
Conclusions:
- Euglena mitochondria possess a specific, ATP-dependent system for cobalamin uptake.
- The internalized cobalamin is tightly bound by soluble mitochondrial proteins, suggesting roles in metabolism.
- This system highlights the intricate mechanisms for essential nutrient acquisition within organelles.