Instrumentation and procedures for real time measurements of proton motive force, membrane potential, delta pH, proton extrusion, and oxygen uptake in respiring cells and vesicles

A monitoring system for energy transduction by bacteriorhodopsin liposomes

A computer-controlled system and custom software are described that collect information and perform computations to quantify important parameters of energy transduction during the conversion of photons into a proton electrochemical gradient (delta mu H+) by bacteriorhodopsin (BR)-liposomes. The strong actinic light used to energize the BR-liposomes causes several serious problems for the approaches commonly used to measure these parameters. This paper identifies these problems and presents solutions that permit the acquisition of the desired information, namely, the initial (1st sec) rate and total extent of H+ translocation, rate of H+ leakage (driven by an existing delta mu H+), external, internal and delta pH values, and delta psi values. The system is presented with representative experimental data.

Comparison of energy-transducing capabilities of the two- and three-subunit cytochromes aa3 from Paracoccus denitrificans and the 13-subunit beef heart enzyme

In the accompanying paper, we have shown that the two-subunit cytochrome aa3 isolated from Paracoccus denitrificans displays the same kind of complex and interactive redox behavior as the 13-subunit cytochrome aa3 from beef heart. Therefore, the redox characteristics are not dependent on the additional 11 subunits. In the current work, we have examined the energy-transducing capabilities of both the two- and three-subunit enzymes obtained from Paracoccus denitrificans in relation to that of the 13-unit mammalian enzyme. We have found that in all of the tested functions, which included the development of delta psi and delta pH, and the pumping of protons, that the two-subunit enzyme is at least as efficient as the structurally more complex mammalian enzyme. There is thus a correlation between the complex redox behavior and energy transducing capabilities of the two enzymes. There was also no difference in energy-transducing capabilities between the two- and three-subunit forms of the bacterial enzyme. It seems that only 2 subunits are required for an efficient energy-transducing cytochrome aa3. The most likely role of the additional subunits in the mammalian enzyme, therefore, seems to be in regulation.

Magainin 2 amide and analogues. Antimicrobial activity, membrane depolarization and susceptibility to proteolysis

We compared the abilities of synthetic magainin 2 amide and its analogues to inhibit the growth of Escherichia coli and to cause membrane depolarization in E. coli cells and cytochrome oxidase liposomes. The analogue, magainin A, was about 40-times more active than magainin 2 amide in inhibiting the growth of E. coli and had a much more sustained effect on the membrane potential. In the liposomal system, however, there was only approx. 20% difference between these two peptides in the reduction of membrane potential and uncoupling of respiration. Studies with pronase digestion suggested that the difference in potency may be due to differential susceptibility to proteolysis in the presence of membranes.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine inhibits proton motive force in energized liver mitochondria

It is known that 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which induces Parkinson's-like disease in primates and humans, depletes hepatocytes of ATP and subsequently causes cell death. Incubation of rat liver mitochondria with MPTP and 1-methyl-4-phenyl pyridinium ion (MPP+) significantly inhibited incorporation of 32Pi into ATP.MPTP and MPP+ inhibited the development of membrane potential and pH gradient in energized rat liver mitochondria, suggesting that reduction of the proton motive force may have reduced ATP synthesis. Since deprenyl, an inhibitor of monoamine oxidase, prevented the formation of MPP+ and inhibited the decrease in membrane potential caused by MPTP, but not that caused by MPP+, these effects of MPTP, as well as cell death, probably were mediated by MPP+. This mechanism may play a role in the specific loss of dopaminergic neurons resulting in MPTP-induced Parkinson's disease.

Direct measurement of the initial proton extrusion to oxygen uptake ratio accompanying succinate oxidation by rat liver mitochondria

The problem of obtaining very early ratios for the H+/O stoichiometry accompanying succinate oxidation by rat liver mitochondria was attacked using new techniques for direct measurement rather than extrapolations based on data obtained after mixing and the recovery of the electrode from initial injection of O2. Respiration was quickly initiated in a thoroughly mixed O2-containing suspension of mitochondria under a CO atmosphere by photolysis of the CO-cytochrome c oxidase complex-. Fast responding O2 and pH electrodes were used to collect data every 10 ms. The response time for each electrode was experimentally measured in each experiment and suitable corrections for electrode relaxations were made. With uncorrected data obtained after 0.8 s, the extrapolation back to zero time on the basis of single-exponential curve fitting confirmed values close to 8.0 as previously reported (Costa et al., 1984). The data directly obtained, however, indicate an initial burst in H+/O ratio that peaked to values of approximately 20 to 30 prior to 50 ms and which was no longer evident after 0.3 s. Newer information and considerations that place all extrapolation methods in question are discussed.

The H+/O ratio of proton translocation linked to the oxidation of succinate by mitochondria. Reply to a commentary

Costa, L.E., Reynafarje, B. and Lehninger, A.L. [(1984) J. Biol. Chem. 259, 4802-4811] have reported 'second-generation' measurements of the H+/O ratio approaching 8.0 for vectorial H+ translocation coupled to succinate oxidation by rat liver mitochondria. In a Commentary in this Journal [Krab, K., Soos, J. and Wikström, M. (1984) FEBS Lett. 178, 187-192] it was concluded that the measurements of Costa et al. significantly overestimated the true H+/O stoichiometry. It is shown here that the mathematical simulation on which Krab et al. based this claim is faulty and that data reported by Costa et al. had already excluded the criticism advanced by Krab et al. Also reported are new data, obtained under conditions in which the arguments of Krab et al. are irrelevant, which confirm that the H+/O ratio for succinate oxidation extrapolated to level flow is close to 8.

A polyvinylchloride-membrane based anion selective electrode for continuous registration of delta pH (interior alkaline) with salicylate as the indicator probe

An anion sensitive electrode has been constructed with the use of the lipid soluble cation benzyl-dimethyl-hexadecylammonium analogous to the procedure described for tetraphenylphosphonium-sensitive electrodes [Shinbo, T., Kamo, N., Kurihara, K. and Kobatake, Y. (1978) Arch. Biochem. Biophys. 187, 414-422]. The anion electrode responds to salicylate concentrations above 400 microM with a Nernstian sensitivity. Less lipid soluble anions like chloride and phosphate do not interfere. Below 400 microM salicylate the response of the electrode decreases gradually so that the sensitivity of the electrode is less than 10 mV per decade change at concentrations of the anion of 50 microM. A computer program has been developed to fit the electrode response curve with a polynomal function of the fourth power. Additional software-allows calculation of changes in the concentration of the salicylate anion, also under conditions where the sensitivity of the electrode for the anion is not constant. In this way the electrode can be used to measure changes in salicylate concentration that occur in a suspension of bacteria when, upon energization, a pH gradient is generated. 31P nuclear magnetic resonance measurements demonstrated that the pH gradient measured with the salicylate-sensitive electrode in the phototrophic bacterium Rhodopseudomonas sphaeroides is quantitatively correct. The response time of the electrode decreases from 1 min at 20 microM salicylate to 10 s at concentrations greater than or equal to 200 microM.