| Abstrakt: |
Processes of energy transduction were studied in isolated rat liver mitochondria, taken as a possible target for DNA intercalators, which differs from a usual one, associated with nucleic acid metabolism reactions. In the mitochondrial suspension, changes in respiration rates and latent ATPase activity in controlled state were defined in addition to a decrease in respiratory control index (V2/V1) and P/O ratio under the influence of DNA intercalators, benzophenanthridine alkaloid sanguinarine and acridine derivative APhMA. Within the range of examined sanguinarine and APhMA concentrations, the increase in respiration rate and activation of latent ATPase activity of mitochondrial suspension was first determined, with the maxima of these activities at 10(-4) M for both the agents. A further increase in sanguinarine and APhMA concentrations caused the inhibition of these reactions. Such dose-dependent shapes, with a maximum for the curves of mitochondrial respiration rate and ATPase activity "bell-shaped"), are typical for the majority of so far known uncouplers of oxidative phosphorylation in mitochondria. The fall of V2/V1 and P/O, under the influence of sanguinarine and APhMA, evidenced for the inhibition of ATP synthesis in mitochondria. The mechanism of uncoupling by sanguinarine and APhMA was supposed to differ from that by protonophores. It has been suggested that the uncoupling of oxidative phosphorylation by sanguinarine and APhMA was associated with the ability of these organic cations to neutralize negative charges near the external side of energized internal mitochondrial membranes. Correlation between the capacity for DNA intercalation and that for the energy transfer inhibition in mitochondria of these two agents is presumably based on the importance of positive charges and hydrophobic interactions, both for intercalation into polynucleotide double helices and for negative charges neutralization in energized mitochondrial membranes. Among DNA intercalators, so far examined, no agent has been established, which would not disturb the coupling of respiration and phosphorylation in mitochondria. However, there is no strong correlation for the agents between the ability to intercalate into DNA double helix and to disturb the energy transfer processes in mitochondria. Sanguinarine, which is more potent, as a DNA intercalator, than APhMA, is weaker than APhMA as an uncoupler of mitochondrial oxidative phosphorylation. For DNA-intercalation, the steric conformity between sizes of the intercalator molecule and of DNA base pairs is of great importance. On the other hand, for mitochondrial energy transfer disturbance, the agent ability to achieve sites of negative charges in the energized inner membranes is more significant. |
