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The electron-transport system of mitochondria from the slime mould Physarum polycephalum
Abstract:
A method is described for the preparation of mitochondria from the slime mould Physarum polycephalum; the mitochondria were not coupled. P. polycephalum mitochondria oxidized added NADH via a rotenone-insensitive pathway, but the oxidation of malate plus glutamate was rotenone sensitive; both of these substrates reduced much less cytochrome b than did succinate, in both aerobic and anaerobic steady states. Spectroscopy at 77 degrees K separated three absorption maxima in the alpha-band region, at 560nm, 553nm and one at 547nm due to cytochrome c. The absorption at 553nm was increased in the aerobic steady state by the addition of 2-heptyl-4-hydroxyquinoline N-oxide, suggesting that it was due to a b-type cytochrome. All three absorption maxima appeared in the aerobic steady state after the addition of a range of substrates. The respiratory activity with different substrates and the response to inhibitors of respiration were similar to those previously described for fungus mitochondria (Weiss et al., 1970; Erickson & Ashworth, 1969). When grown under conditions of haem limitation the mitochondria contained a lower concentration of cytochromes than normal.
Insights
Mitochondria from slime mould Physarum polycephalum were isolated and characterized. Their respiratory activity and cytochrome content were analyzed, revealing similarities to fungal mitochondria.
Area of Science:
- Biochemistry
- Cell Biology
- Mycology
Background:
- Mitochondria are crucial for cellular respiration.
- Slime moulds, like Physarum polycephalum, offer unique models for studying cellular processes.
- Understanding mitochondrial function in diverse organisms is key to evolutionary and metabolic studies.
Purpose of the Study:
- To describe a method for isolating functional mitochondria from Physarum polycephalum.
- To characterize the respiratory properties and cytochrome composition of these mitochondria.
- To compare Physarum mitochondria with those from other organisms, particularly fungi.
Main Methods:
- Isolation of mitochondria from Physarum polycephalum.
- Measurement of mitochondrial respiratory activity using various substrates (NADH, malate plus glutamate, succinate).
- Spectroscopic analysis (at 77 K) to identify and quantify cytochromes (cytochrome b, cytochrome c).
- Assessment of inhibitor responses (rotenone, 2-heptyl-4-hydroxyquinoline N-oxide).
Main Results:
- Isolated Physarum polycephalum mitochondria were not coupled.
- NADH oxidation was rotenone-insensitive, while malate plus glutamate oxidation was rotenone-sensitive.
- Both substrates reduced less cytochrome b compared to succinate.
- Spectroscopy identified three alpha-band absorption maxima, including one attributed to cytochrome b.
- Respiratory activity and inhibitor responses resembled those of fungal mitochondria.
- Haem-limited growth resulted in lower mitochondrial cytochrome concentrations.
Conclusions:
- Physarum polycephalum mitochondria possess distinct respiratory pathways.
- The cytochrome composition and respiratory behavior show similarities to fungal mitochondria.
- Mitochondrial cytochrome levels are influenced by haem availability during growth.