Mitochondria contain a potassium specific channel (mitoKATP channel) sensitive to ATP and antidiabetic sulfonylureas. The mitochondrial Katp channel plays an important role in the mitochondrial volume control and in regulation of the components of protonmotive force. This minireview describes the properties and current hypotheses concerning the function of mitoKATP channel.
The mitochondrial DNA (mtDNA) polymerase was isolated from a protease-deficient yeast strain (PY2), and purified about 3000 fold by a column chromatography on phosphocellulose, heparin-agarose, and single-stranded DNA cellulose. The purified polymerase was characterized with respect to optimal nucleotide concentration, template-primer specificity and sensitivity to some inhibitors. These results were compared with the nuclear DNA polymerase I activity. Both polymerases showed similar requirement of deoxynucleotide concentrations (Km < 1 uM), and highest activity with poly(dA-dT) template. However, the mtDNA polymerase was more sensitive to ddTTP, EtBr and Mn2+ inhibition in comparison to the nuclear DNA polymerase I. The mtDNA polymerase did not need ATP as an energy source for in vitro DNA synthesis. This mtDNA polymerase preparation also showed 3' -> 5' exonudease activity.
Several parasitic plants are known to have acquired mitochondrial genes via a horizontal transfer from their hosts. However, mitochondrial gene transfer in this direction has not yet been found in the parasite-rich family Orobanchaceae. Based on a phylogenetic analysis of the mitochondrial atp6 gene in selected species of Orobanche s.l., we provide evidence of a host-to-parasite transfer of this gene in O. coerulescens, which is a Eurasiatic species that parasitises Artemisia (Asteraceae). We did not find the original Orobanche atp6 gene in this species, which suggests that it has been replaced by a gene that was acquired from Asteraceae. In addition, our data suggest the occurrence of a second HGT event in the atp6 sequence – from Asteraceae to Phelipanche. Our results support the view that the transfer of genetic material from hosts to parasites influences the mitochondrial genome evolution in the latter.
The science of toxicology today has reached a stage where the change from exploration of biological responses to xenobiotics in terms of phenomenology, to mechanistic explanations based on molecular logistics is quite apparent. A conceptual mechanism regarding unity and diversity of stress has been proposed by our laboratory. Generation of free radicals leading to membrane damage and alterations in calcium homeostasis seems to be the common unspecific mechanism in toxic responses which may lead to cell death. Changes in the mitochondrial structure and functions due to chemical or oxidative stress gives mechanistic clues and is an ideal system for studying such a phenomenon. Mitochondrial responses to some chemical agents with respect to its redox equilibrium are presented here.
c-type cytochromes are characterized by the presence of two covalent bonds linking heme to apocytochrome and by the heme attachment motif in the apoprotein. Several molecular systems for the maturation of c-type cytochromes have evolved in different organisms. The best characterized are three of them: system I, system II and system III. Heme is synthesized in bacterial cytoplasm, in plastids, and in animal and fungal mitochondria. Therefore the maturation of bacterial and plastid c-type cytochromes involves the transport of heme and apocytochrome from the n-side to the p-side of the respective biological membranes and the formation of the covalent bond at the p-side. It should be underlined that the site of the c-type apocytochrome synthesis is also distinct from the site of its functioning. The aim of this review is to present the current state of knowledge concerning the structure and function of two systems – system I and system II – in the maturation of plant mitochondrial and plastid c-type cytochromes, respectively.
There are many theories of aging and a number of them encompass the role of mitochondria in this process. Mitochondrial DNA mutations and deletions have been shown to accumulate in many tissues in mammals during aging. However, there is little evidence that these mutations could affect the functioning of aging tissues.
The purpose of this study was to examine the effects of oxidative stress caused by hydroperoxide (H2O2) in the presence of iron ions (Fe2+) on mitochondria of the amoeba Acanthamoeba castellanii. We used isolated mitochondria of A. Castellanii and exposed them to four levels of H2O2 concentration: 0.5, 5, 15, and 25 mM. We measured basic energetics of mitochondria: oxygen consumption in phosphorylation state (state 3) and resting state (state 4), respiratory coefficient rates (RC), ADP/O ratios, membrane potential (ΔΨm), ability to accumulate Ca2+ , and cytochrome crelease. Our results show that the increasing concentrations of H2O2 stimulates respiration in states 3 and 4. The highest concentration of H2O2 caused a 3-fold increase in respiration in state 3 compared to the control. Respiratory coefficients and ADP/O ratios decreased with increasing stress conditions. Membrane potential significantly collapsed with increasing hydroperoxide concentration. The ability to accumulate Ca2+ also decreased with the increasing stress treatment. The lowest stress treatment (0.5 mM H2O2) significantly decreased oxygen consumption in state 3 and 4, RC, and membrane potential. The ADP/O ratio decreased significantly under 5 mM H2O2 treatment, while Ca2+ accumulation rate decreased significantly at 15 mM H2O2. We also observed cytochrome crelease under increasing stress conditions. However, this release was not linear. These results indicate that as low as 0.5 mM H2O2 with Fe2+ damage the basic energetics of mitochondria of the unicellular eukaryotic organism Acanthamoeba castellanii