Redox state-dependent aggregation of mitochondria induced by cytochrome c

Is the mitochondrial ATP synthesis solely H+-driven, K+,H+ symport-driven or K+/H+ antiport-driven?

Some recent literature experimental data indicate that the mitochondrial ATP synthesis might be not solely H+-driven, but K+,H+ symport-driven membrane potential-dependent, considered as a further development of Mitchell's chemiosmotic theory, in contrast to the anti-Mitchell's hypothesis of K+/H+ antiport-driven mechanism. In this short communication, the attention was pointed to a possible influence of the ionic strength of the used KCl incubation medium, versus of only K+ ions, and of the Mg2+-induced mitochondrial aggregation in the sucrose medium on the reported rates of the mitochondrial respiration and ATP synthesis. These observations were based on the own author's experimental works published earlier.

Effect of betulin and betulonic acid on isolated rat liver mitochondria and liposomes

The paper considers the effects of plant triterpenoid betulin and its derivative betulonic acid on rat liver mitochondria and liposomes. It was found that betulonic acid and, to a lesser extent, betulin, activate mitochondrial respiration in states 2 and 4 and inhibit ADP- and DNP-stimulated (uncoupled) respiration. The effect of betulonic acid resulted in a significant decrease of the respiratory control and ADP/O ratios and decrease in Δψ. The effects of both compounds were most pronounced in the case of succinate-fueled mitochondrial respiration. This may include both the possible protonophore effect of betulonic acid and the inhibition of respiratory chain complexes by both compounds. Both agents enhanced H₂O₂ production in succinate-fueled mitochondria, while betulonic acid exerted an antioxidant effect with NAD-dependent substrates. Betulin was found to induce mitochondrial aggregation, but had no effect on membrane permeability. A similar pattern was found on liposomes. As revealed by the laurdan generalized polarization (GP) technique, betulin increased laurdan GP in lecithin liposomes, indicating a decrease in membrane fluidity. Measurements of GP as a function of fluorescence excitation wavelength gave an ascending line for high concentrations of betulin, which can be interpreted as phase heterogeneity of the lipid/betulin system. High concentrations of betulin (> 60 mol%) was also demonstrated to cause permeabilization of lecithin liposomes. Betulonic acid was much less effective in inducing the aggregation of mitochondria and liposomes and had no effect on membrane permeability. The possible mechanisms of betulin and betulonic acid effect on rat liver mitochondria and liposomes are discussed.