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Beta-NADH decreases the permeability of the mitochondrial outer membrane to ADP by a factor of 6
1Department of Zoology, University of Maryland, College Park 20742.
Abstract:
Mitochondria with intact outer membrane (99% intact based on cytochrome c impermeability) were isolated and used to measure the permeability of their outer membrane to ADP. beta-NADH reduced the permeability in a concentration-dependent manner (KD = 87 +/- 5 microM) by a factor of 6. alpha-NADH and beta-NAD+ cannot mimic the action of beta-NADH. The mitochondrial outer membranes become rate-limiting in the presence of beta-NADH at low, physiologically relevant, ADP concentrations (< 30 microM). beta-NADH has been shown to increase the voltage dependence of VDAC (a major pathway for metabolite transport across the outer membrane) in a reconstituted system and this may be the way it acts on the isolated mitochondria. Inhibition of beta-NADH dehydrogenases does not inhibit the action of beta-NADH indicating that it is not acting by delivering reducing equivalents. The ability of beta-NADH, produced by glycolysis, to inhibit mitochondrial function by reducing the permeability of the outer membrane may be one pathway responsible for the Crabtree effect.
Insights
Beta-NADH, a molecule produced during glycolysis, significantly reduces mitochondrial outer membrane permeability to ADP. This finding suggests a novel mechanism contributing to the Crabtree effect, impacting cellular energy regulation.
Area of Science:
- Cellular respiration
- Mitochondrial function
- Metabolic regulation
Background:
- Mitochondria are key organelles for cellular energy production.
- The permeability of the mitochondrial outer membrane regulates metabolite transport.
- The Crabtree effect describes enhanced glycolysis under aerobic conditions in certain cells.
Purpose of the Study:
- To investigate the effect of beta-NADH on mitochondrial outer membrane permeability to ADP.
- To elucidate the mechanism by which beta-NADH influences mitochondrial function.
- To explore the potential role of beta-NADH in the Crabtree effect.
Main Methods:
- Isolation of mitochondria with intact outer membranes (99% purity).
- Measurement of outer membrane permeability to ADP in the presence of varying beta-NADH concentrations.
- Assessment of beta-NADH's mechanism of action, including VDAC voltage dependence and beta-NADH dehydrogenase inhibition.
Main Results:
- Beta-NADH reduced outer membrane permeability to ADP in a concentration-dependent manner (KD = 87 +/- 5 microM) by a factor of 6.
- Alpha-NADH and beta-NAD+ did not replicate this effect.
- Mitochondrial outer membranes became rate-limiting for ADP transport at low, physiological ADP concentrations (< 30 microM) in the presence of beta-NADH.
- Beta-NADH's action was independent of beta-NADH dehydrogenases, suggesting it does not act via reducing equivalents.
Conclusions:
- Beta-NADH directly inhibits mitochondrial outer membrane permeability to ADP.
- This inhibition may occur through modulation of Voltage-Dependent Anion Channels (VDAC).
- The ability of beta-NADH to reduce mitochondrial function offers a potential explanation for the Crabtree effect.