Journal of bioenergetics

Quinones such as ubiquinone are the lipid soluble electron and proton carriers in the membranes of mitochondria, chloroplasts and oxygenic bacteria. Quinones undergo controlled redox reactions bound to specific sites in integral membrane proteins such as the cytochrome bc1 oxidoreductase. The quinone reactions in bacterial photosynthesis are amongst the best characterized, presenting a model to understand how proteins modulate cofactor chemistry. The free energy of ubiquinone redox reactions in aqueous solution and in the QA and QB sites of the bacterial photosynthetic reaction centers (RCs) are compared. In the primary QA site ubiquinone is reduced only to the anionic semiquinone (Q•−) while in the secondary QB site the product is the doubly reduced, doubly protonated quinol (QH2). The ways in which the protein modifies the relative energy of each reduced and protonated intermediate are described. For example, the protein stabilizes Q•− while destabilizing Q= relative to aqueous solution through electrostatic interactions. In addition, kinetic and thermodynamic mechanisms for stabilizing the intermediate semiquinones are compared. Evidence for the protein sequestering anionic compounds by slowing both on and off rates as well as by binding the anion more tightly is reviewed.

Inactivation of the membrane-bound ATPase by tight ADP binding was studied under nonenergized conditions. The energy state of the system was controlled either by omitting MgCl2, preventing ATP hydrolysis, or by addition of an uncoupler which dissipates the $$\Delta \overline \mu _{{\rm H}^ + } $$ . In the absence of Mg2+, ATP prevents the inactivation of the enzyme by ADP, in a competitive manner. This effect of ATP resembles that of GDP with Mg2+ present. In the presence of nigericin, Mg2+, and ATP, inactivation occurs after a 10–15-sec interval, during which the enzyme is able to hydrolyze ATP at a relatively rapid rate. The degree of inactivation is proportional to the level of bound ADP detected. This behavior is different from that of the coupled ATPase (no uncoupler added), where inactivation is attained only upon exhaustion of the ATP by its hydrolysis, despite the finding that ADP binds tightly to the active ATPase at all stages of the reaction. Higher levels of tightly bound ADP were detected in the presence of an uncoupler. We suggest that the interval during which the enzyme becomes inactive is that required for the enzyme to generate and bind ADP, and to change from the active to the inactive conformation. These results support the mechanism suggested previously for the modulation of the ATPase by tight nucleotide binding.

The respiration rate of Pi-deprived cells ofMicrococcus lysodeikticus is markedly increased by Pi, and returns to the original level following Pi consumption. The stimulation of the respiration was found to be specific for Pi and arsenate. Although succinate and valinomycin enchanced the respiration of both Pi-grown and Pi-deprived cells, only the latter could be further stimulated by Pi. The effect of Pi on the respiration rate was found to be concentration dependent. The control of respiration by Pi is due to its rapid uptake and its subsequent polymerization to polyphosphate via ATP. Both of these processes are coupled to proton influx into the cell, and thus stimulate the proton efflux and the respiration rate.

Genomic data regarding the nucleoside diphosphate (NDP) kinase genes have been accumulated from diverged phyla. Comparison of their regulatory sequences have shed light on the multiple facets of gene regulation systems. Phylogenetic studies, including CpG island and intron-mapping, and homologous sequence comparison, have suggested that the regions of the major mammalian genes, the ortholog (rat α or nm23-H2) and its paralog (rat β or nm23-H1), have been constructed by a stepwise gain and loss of alien genes resulting in “multiple-layered” regulatory systems. They contain representative cis-elements for the constitutive, stage/lineage-specific, and early response expression. These elements' binding capacities to nuclear proteins were confirmed by electrophoretic mobility shift assay. Further, these regulatory systems generate heterogeneous mRNA at the 5′ untranslated region, which influences their own translation efficiencies. In terms of this process, the transcription system would control another layer of gene expression: posttranscriptional (translational) regulation.

Schizophrenia etiology is unknown, nevertheless imbalances occurring in an acute psychotic episode are important to its development, such as alterations in cellular energetic state, REDOX homeostasis and intracellular Ca2+ management, all of which are controlled primarily by mitochondria. However, mitochondrial function was always evaluated singularly, in the presence of specific respiratory substrates, without considering the plurality of the electron transport system. In this study, mitochondrial function was analyzed under conditions of isolated or multiple respiratory substrates using brain mitochondria isolated from MK-801-exposed mice. Results showed a high H2O2 production in the presence of pyruvate/malate, with no change in oxygen consumption. In the condition of multiple substrates, however, this effect is lost. The analysis of Ca2+ retention capacity revealed a significant change in the uptake kinetics of this ion by mitochondria in MK-801-exposed animals. Futhermore, when mitochondria were exposed to calcium, a total loss of oxidative phosphorylation and an impressive increase in H2O2 production were observed in the condition of multiple substrates. There was no alteration in the activity of the antioxidant enzymes analyzed. The data demonstrate for the first time, in an animal model of psychosis, two important aspects (1) mitochondria may compensate deficiencies in a single mitochondrial complex when they oxidize several substrates simultaneously, (2) Ca2+ handling is compromised in MK-801-exposed mice, resulting in a loss of phosphorylative capacity and an increase in H2O2 production. These data favor the hypothesis that disruption of key physiological roles of mitochondria may be a trigger in acute psychosis and, consequently, schizophrenia.

2-Arachidonoylglicerol (2-AG) là một endocannabinoid mô phỏng các tác động dược lý của Δ9 tetrahydrocannabinol, thành phần gây tác động tâm lý của cây Cannabis sativa. Chất này có mặt trong nhiều mô động vật có vú như não, gan, lá lách, tim và thận, nơi mà nó có các tác động sinh học khác nhau, có thể thông qua thụ thể hoặc độc lập với sự kích hoạt thụ thể. Công trình này phân tích tác động của 2-AG lên chức năng ty thể gan. Kết quả cho thấy rằng 2-AG gây ra sự giảm đáng kể giải phóng cytochrome c nhạy cảm với ciclosporin A, được kích thích bởi canxi từ ty thể, một quá trình đại diện cho một sự kiện sớm của chương trình thải hợp bào chết. Sự sưng nở ma trận và sản xuất ROS nhạy cảm với ciclosporin, được đo dưới cùng điều kiện này, thì ngược lại, gần như không bị ảnh hưởng hoặc thậm chí tăng lên, theo thứ tự, bởi 2-AG. Hơn nữa, 2-AG được phát hiện kích thích hoạt động succinate oxidase ở trạng thái nghỉ và ức chế hoạt động ATP synthase FoF1 nhạy cảm với oligomycin. Tất cả các tác động này dường như liên quan đến việc thay đổi độ lỏng của màng ty thể phụ thuộc vào 2-AG, đã được đo lường thông qua sự phân cực tổng quát của huỳnh quang laurdan.

The arrangement and movement of mitochondria were quantitatively studied in adult rat cardiomyocytes and in cultured continuously dividing non beating (NB) HL-1 cells with differentiated cardiac phenotype. Mitochondria were stained with MitoTracker® Green and studied by fluorescent confocal microscopy. High speed scanning (one image every 400 ms) revealed very rapid fluctuation of positions of fluorescence centers of mitochondria in adult cardiomyocytes. These fluctuations followed the pattern of random walk movement within the limits of the internal space of mitochondria, probably due to transitions between condensed and orthodox configurational states of matrix and inner membrane. Mitochondrial fusion or fission was seen only in NB HL-1 cells but not in adult cardiomyocytes. In NB HL-1 cells, mitochondria were arranged as a dense tubular network, in permanent fusion, fission and high velocity displacements of ~90 nm/s. The differences observed in mitochondrial dynamics are related to specific structural organization and mitochondria-cytoskeleton interactions in these cells.

The ATP synthase of the yeast Saccharomyces cerevisiae is composed of 20 different subunitswhose primary structure is known. The organization of proteins that constitute the membranousdomain is now under investigation. Cysteine insertions combined with the use of nonpermeantmaleimide reagents and cross-linking reagents showing different lengths and specificitycontribute to the knowledge of the location of the N- and C-termini of the subunits involved in thestator of the enzyme and their organization. This review summarizes data on yeast ATP synthaseobtained in our laboratory since 1980.

Fatty acid-binding protein 3 (FABP3) is a low molecular weight protein with distinct tissue distribution, which may play an important role in fatty acid transport, cell growth, cellular signaling, and gene transcription. We have previously shown FABP3 was more highly expressed in myocardium with ventricular septal defects than in normal myocardium and furthermore, that overexpression of FABP3 causes mitochondrial dysfunction and induces apoptosis in the P19 mouse teratocarcinoma cell line (P19), which is a suitable model for the investigation of cardiac differentiation at the molecular and functional levels. α-Lipoic acid (α-LA), a natural dithiol compound with antioxidant properties, has been reported to protect mitochondrial function in cells. In this study, we established an FABP3-overexpressing P19 cell line for the investigation of the impact of α-LA on mitochondrial impairment and apoptosis in these cells. Mitochondrial morphology was evaluated by transmission electron microscopy, while the effects of α-LA on reactive oxygen species (ROS) production, mitochondrial membrane potential (MMP), intracellular ATP content and the amount of mitochondrial DNA were analyzed by flow cytometry, a commercially available assay and quantitative real-time PCR, respectively. The results revealed that α-LA ameliorated mitochondrial deformation and decreased intracellular ROS production. Furthermore, the MMP, intracellular ATP synthesis and the amount of mitochondrial DNA were also increased. Most significantly, α-LA was shown to reverse apoptosis. Collectively, our results indicate that abnormalities in FABP3 expression contribute to mitochondrial dysfunction and apoptosis, and that α-LA represents a suitable candidate for development as a treatment for apoptosis-related congenital cardiac malformations.