Studies of protein-phospholipid interaction in isolated mitochondrial ubiquinone-cytochrome c reductase

Contribution of mitochondria to injury of hepatocytes and liver tissue by hyperthermia

OBJECTIVE

The aim of this study was to investigate functional changes of liver mitochondria within the experimentally modeled transition zone of radiofrequency ablation and to estimate possible contribution of these changes to the energy status of liver cells and the whole tissue.

MATERIALS AND METHODS

Experiments were carried out on mitochondria isolated from the perfused liver and isolated hepatocytes of male Wistar rats. Hyperthermia was induced by changing the temperature of perfusion medium in the range characteristic for the transition zone (38-52°C). After 15-min perfusion, mitochondria were isolated to investigate changes in the respiration rates and the membrane potential. Adenine nucleotides extracted from isolated hepatocytes and perfused liver subjected to hyperthermic treatment were analyzed by HPLC.

RESULTS

Hyperthermic liver perfusion at 42-52°C progressively impaired oxidative phosphorylation in isolated mitochondria. Significant inhibition of the respiratory chain components was observed after perfusion at 42°C, irreversible uncoupling became evident after liver perfusion at higher temperatures (46°C and above). After perfusion at 50-52°C energy supplying function of mitochondria was entirely compromised, and mitochondria turned to energy consumers. Hyperthermia-induced changes in mitochondrial function correlated well with changes in the energy status and viability of isolated hepatocytes, but not with the changes in the energy status of the whole liver tissue.

CONCLUSIONS

In this study the pattern of the adverse changes in mitochondrial functions that are progressing with increase in liver perfusion temperature was established. Results of experiments on isolated mitochondria and isolated hepatocytes indicate that hyperthermic treatment significantly and irreversibly inhibits energy-supplying function of mitochondria under conditions similar to those existing in the radiofrequency ablation transition zone and these changes can lead to death of hepatocytes. However, it was not possible to estimate contribution of mitochondrial injury to liver tissue energy status by estimating only hyperthermia-induced changes in adenine nucleotide amounts on the whole tissue level.

Interaction between cytochrome caa3 and F1F0-ATP synthase of alkaliphilic Bacillus pseudofirmus OF4 is demonstrated by saturation transfer electron paramagnetic resonance and differential scanning calorimetry assays

Interaction between the cytochrome caa3 respiratory chain complex and F1F0-ATP synthase from extremely alkaliphilic Bacillus pseudofirmus OF4 has been hypothesized to be required for robust ATP synthesis by this alkaliphile under conditions of very low protonmotive force. Here, such an interaction was probed by differential scanning calorimetry (DSC) and by saturation transfer electron paramagnetic resonance (STEPR). When the two purified complexes were embedded in phospholipid vesicles individually [(caa3)PL, (F1F0)PL)] or in combination [(caa3 + F1F0)PL] and subjected to DSC analysis, they underwent exothermic thermodenaturation with transition temperatures at 69, 57, and 46/75 degrees C, respectively. The enthalpy change, deltaH (-8.8 kcal/mmol), of protein-phospholipid vesicles containing both cytochrome caa3 and F1F0 was smaller than that (-12.4 kcal/mmol) of a mixture of protein-phospholipid vesicles formed from each individual electron transfer complex [(caa3)PL + (F1F0)PL]. The rotational correlation time of spin-labeled caa3 (65 micros) in STEPR studies increased significantly when the complex was mixed with F1F0 prior to being embedded in phospholipid vesicles (270 micros). When the complexes were reconstituted separately and then mixed together, or either mitochondrial cytochrome bc1 or F1F0 was substituted for the alkaliphile F1F0, the correlation time was unchanged (65-70 micros). Varying the ratio of the two alkaliphile complexes in both the DSC and STEPR experiments indicated that the optimal stoichiometry is 1:1. These results demonstrate a physical interaction between the cytochrome caa3 and F1F0-ATP synthase from B. pseudofirmus OF4 in a reconstituted system. They support the suggestion that such an interaction between these complexes may contribute to sequestered proton transfers during alkaliphile oxidative phosphorylation at high pH.

Co-enzyme Q10: a new drug for cardiovascular disease

Co-enzyme Q10 (ubiquinone) is a naturally occurring substance which has properties potentially beneficial for preventing cellular damage during myocardial ischemia and reperfusion. It plays a role in oxidative phosphorylation and has membrane stabilizing activity. The substance has been used in oral form to treat various cardiovascular disorders including angina pectoris, hypertension, and congestive heart failure. Its clinical importance is now being established in clinical trails worldwide.

Phospholipid specificity of bovine heart bc1 complex

Bovine heart bc1 complex was reversibly inactivated by a new simple and effective chromatographic delipidation method. Upon phospholipid replenishment, catalytic activity increased from values near zero to values 2-6-times higher than those of the original preparation. Compared to original preparations maximally activated by additional phospholipid, the degree of reactivation was up to 100%. By this delipidation method, the 6.4-kDa protein subunit was removed with the phospholipid. The loss of this protein neither diminished electron transport activity nor abolished proton translocation. Two requirements were necessary to obtain quantitative data: (a) only bc1 complexes, homogeneously dissolved before and after relipidation had to be used and (b) the phospholipid bound to the complex had to be determined. The correlation of catalytic activity to bound phospholipid was studied in the range of low phospholipid/protein ratios, which had previously been insufficiently resolved. Catalytic activity increased linearly with added phospholipid up to a molar ratio of 80-100 lipid molecules/dimeric complex. This corresponds to the number of phospholipid molecules that complete a single bilayer annulus. The activating effect of phospholipid is not merely due to a hydrophobic phase effect, since it strongly depends on the nature of the polar head group of the added phospholipid. Of the three major phospholipids bound to the bc1 complex, only phosphatidylethanolamine and phosphatidylcholine activated when added as sole phospholipid. Tightly bound diphosphatidylglycerol was needed for preservation of the native complex structure.