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Changes in intramitochondrial adenine nucleotides in blowfly flight-muscle mitochondria
Abstract:
1. With freshly isolated blowfly mitochondria 38% of the intramitochondrial adenine nucleotide was present as AMP. 2. On incubation with oxidizable substrates the AMP and ADP concentrations fell and that of ATP rose; with pyruvate together with proline the ATP concentration reached its maximum value at 6min; with glycerol phosphate the phosphorylation of endogenous nucleotide was more rapid. 3. Addition of the uncoupling agent carbonyl cyanide phenylhydrazone caused a rapid fall of ATP and a parallel rise in ADP, then ADP was converted into AMP. 4. This was in contrast with rat liver mitochondria endogenous AMP concentrations, which were always lower than those of blowfly mitochondria and changed little under different metabolic conditions. 5. Evidence is presented that adenylate kinase (EC 2.7.4.3) has a dual distribution in blowfly mitochondria, a part being located in the matrix space and a part in the space between the outer and inner mitochondrial membranes, as in liver and other mitochondria. 6. The possible regulatory role of changing AMP concentrations in the mitochondrial matrix was investigated. Partially purified pyruvate carboxylase (EC 6.4.1.1) and citrate synthase (EC 4.1.3.7) were inhibited 30% by 2mm-AMP, whereas pyruvate dehydrogenase (EC 1.2.4.1) was unaffected. 7. AMP activated the NAD(+)-linked isocitrate dehydrogenase (EC 1.1.1.41) activity of blowfly mitochondria in the absence of ADP, but in the presence of ADP, AMP caused inhibition. 8. It is suggested that AMP may exert a controlling effect on the oxidative activity of blowfly mitochondria.
Insights
Blowfly mitochondria have high AMP levels that decrease with substrate oxidation, unlike rat liver mitochondria. AMP influences key enzymes, suggesting a regulatory role in mitochondrial oxidative activity.
Area of Science:
- Biochemistry
- Mitochondrial Physiology
Background:
- Mitochondria are crucial for cellular energy production.
- Adenine nucleotide levels (ATP, ADP, AMP) are vital indicators of mitochondrial metabolic state.
- Blowfly mitochondria exhibit unique metabolic characteristics compared to mammalian models.
Purpose of the Study:
- To investigate the adenine nucleotide composition and metabolic regulation within blowfly mitochondria.
- To compare AMP levels and dynamics in blowfly versus rat liver mitochondria.
- To explore the regulatory role of AMP on mitochondrial enzyme activity.
Main Methods:
- Isolation and incubation of blowfly mitochondria with oxidizable substrates.
- Measurement of intramitochondrial adenine nucleotide concentrations (ATP, ADP, AMP).
- Assay of adenylate kinase distribution and its effect on key mitochondrial enzymes.
Main Results:
- Freshly isolated blowfly mitochondria contained 38% AMP; substrate oxidation reduced AMP and ADP while increasing ATP.
- Uncoupling agent addition caused ATP hydrolysis to ADP and then AMP.
- AMP concentrations were higher and more dynamic in blowfly mitochondria than rat liver mitochondria.
- Adenylate kinase showed dual localization (matrix and intermembrane space).
- AMP inhibited pyruvate carboxylase and citrate synthase but activated NAD(+)-linked isocitrate dehydrogenase in the absence of ADP.
Conclusions:
- AMP plays a significant role in regulating blowfly mitochondrial oxidative activity.
- The high AMP levels and its regulatory function suggest specific adaptations in blowfly energy metabolism.
- AMP's differential effects on enzymes highlight its complex role in metabolic control within mitochondria.