Beta-NADH decreases the permeability of the mitochondrial outer membrane to ADP by a factor of 6.

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.