Photosynthetic activity and components of the electron transport chain in the aerobic bacteriochlorophyll <Emphasis Type="Italic">a</Emphasis>-containing bacterium <Emphasis Type="Italic">Roseinatronobacter thiooxidans</Emphasis>

Bioenergetics of the aerobic bacteriochlorophyll a-containing (BCl a) bacterium (ABC bacterium) Roseinatronobacter thiooxidans is a combination of photosynthesis, oxygen respiration, and oxidation of sulfur compounds under alkaliphilic conditions. The photosynthetic activity of Rna. thiooxidans cells was established by the photoinhibition of cell respiration and reversible photobleaching discoloration of the BCl a of reaction centers (RC), connected by the chain of electron transfer with cytochrome c ₅₅₁ oxidation. The species under study, like many purple bacteria and some of the known ABC bacteria, possesses a light-harvesting pigment-protein (LHI) complex with the average number of 30 molecules of antenna BCl a per one photosynthetic RC. Under microaerobic growth conditions, the cells contained bc ₁ complex and two terminal oxidases: cbb ₃-cytochrome oxidase and the alternative cytochrome oxidase of the a ₃ type. Besides, Rna. thiooxidans was shown to have several different soluble low- and high-potential cytochromes c, probably associated with the ability of utilizing sulfur compounds as additional electron donors.     

Proton/electron stoichiometry of mitochondrialbc 1 complex. Influence of pH and transmembrane δpH

The effect of pH and transmembrane pH on the efficiency of the proton pump of the mitochondrialbc ₁ complex bothin situ and in the reconstituted state was studied. In both cases the H⁺/e ^– ratio for vectorial proton translocation by thebc ₁ complex respiring at the steady state, under conditions in which the transmembrane pH difference (pH) represents the only component of the proton motive force (p), was significantly lower than that measured under level flow conditions. The latter amounts, at neutral pH, to 1 (2 including the scalar H⁺ release). In the reconstituted system steady-state pH was modulated by changing the intravesicular buffer as well as the intra/extra-liposomal pH. Under these conditions the H⁺/e^– ratio varied inversely with the pH. The data presented show that pH exerts a critical control on the proton pump of thebc ₁ complex. Increasing the external pH above neutrality caused a decrease of the level flowH ⁺/e ^– ratio. This effect is explained in terms of proton/electron linkage inb cytochromes.     

Oxygen Uptake and Antioxidant Responses of the Free-Living Diplomonad Hexamita sp.

ABSTRACT. The free-living anaerobic flagellate Hexamita sp. was observed to actively consume O₂ with a K_m O₂ of 13 μM. Oxygen consumption increased lineraly with O₂ tension up to a threshold level of 100 μM, above which it was inhibited. Oxygen uptake was supported by a number of substrates but probably not coupled to energy conservation as cytochromes could not be detected spectro-photometrically. In addition, inhibitors specific for respiratory chain components did not significantly affect O₂ uptake. Respiration was however, partially inhibited by flavoprotein and iron-sulfur protein inhibitors. NAD(P)H supported O₂ consumption was measured in both particulate and soluble fractions; this activity was partially inhibited by quinacrine. A chemosensory response was observed in cells exposed to air, however no response was observed in the presence of superoxide dismutase plus catalase. Catalase and nonspecific peroxidase activity could not be detected, but superoxide dismutase activity was present. Superoxide dismutase was sensitive to NaN₃ and H₂O₂ but not KCN, suggesting a Fe prosthetic group. Flow cytometric analysis revealed that thiol levels in live cells were depleted in the presence of t-butyl H₂O₂. The observed NADPH-driven glutathione reductase activity is believed to recycle oxidized thiols in order to re-establish reduced thiol levels in the cell. The corresponding thiol cycling enzyme glutathione peroxidase could not be detected. The ability to withstand high O₂ tensions (100 μM) would enable Hexamita to spend short periods in a wider range of habitats. Prologed exposure to O₂ tensions higher than 100 μM leads to irreversible damage and cell death.     

Rapid scan spectrometry: oxidation of substrates by coupled potato mitrochondria

By rapid scan spectrometry, spectral changes of redox components have been followed during the oxidation of substrates by coupled potato ( Solanum luberosum L. cv . Bintje) mitochondria under different redox conditions. The redox changes of the b cytochromes, the changes in the base line level and in the slope of the spectra during aerobiosis appear to be connected with changes of the membrane potential. As the latter does not collaps at anaerobiosis, cytochrome o₃ remains in an oxidized state. Collapse of the membrane potential by uncouplers induces partial oxidation of the b cytochromes and reduction of cytochrome a ₃, so that toe resulting redox states derive from thermodynamic equilibrium with the redox conditions of the substrates. However, in aerobiosis as well as in anaerobiosis, the amplitude changes of the b cytochromes vary with the substrate oxidized as if these components were not always completely connected with the cytochrome oxidase complex. The b cytochromes become fuliy reduced only after dithionite reduction.     

Cytochromes of developing plastids of greening barley: Effects of inhibitors of haem synthesis

The properties of the cytochromes of etiolated barley plastids and 20 hr greened barley plastids were examined by potentiometric titration. In etiolate     

The electron transport systems of Fasciola hepatica mitochondria.

The electron transport systems of Fasciola hepatica mitochondria were investigated spectrophotometrically at room temperature and at −196°. The mitochondria were found to contain substrate reducible a-, b- and c-type cytochromes. All of the cytochrome components of the classical mammalian type of respiratory chain were present, although the concentration of cytochromes aa₃ was low. In addition to the mammalian type of respiratory chain, the Fasciola mitochondria contained a substrate reducible b-type cytochrome component (557 nm) which included a CO reactive o-type cytochrome. The results suggest that F. hepatica mitochondria contain a branched electron transport system including a mammalian type of chain and involving two terminal oxidases and at least two b-type cytochromes.     

Determination of the orientation of membrane vesicles derived from mitochondria

Membrane vesicles of physiological as well as inverted orientation can be isolated from mitochrondria. The presence of these vesicles in a membrane can be determined and quantitated by determining the differences between the two vesicle types in terms of rates of NADH oxidation, rates of oxidation of tricarboxylate cycle intermediates, rates of ATP hydrolysis and sensitivity to inhibitors, stimulation of respiration by exogenous cytochromec, inhibition of respiration by polycationic proteins, and visualization of the ATPase by electron microscopy. Procedures to isolate the two membrane types and characteristics of homogeneously oriented preparations are described. Differences in data obtained with homogeneous vesicle preparations and with vesicles of mixed orientation are illustrated. Nonhomogeneously oriented preparations can be enriched in the desired vesicular type by the use of immunoprecipitation, affinity chromatography, and differential centrifugation. The concept of a hybrid vesicle containing oppositely oriented regions is not supported by experimental data.     

Effects of Thiamine Deprivation and Replacement on the Mitochondrion of Polytomella agilis*

SYNOPSIS. Late log-phase cells of Polytomella agilis, grown with or without thiamine, were examined by electron microscopy. The mitochondrial profiles of cells cultivated in the presence of thiamine are relatively few in number and irregular in shape. The inner membranes, randomly dispersed in a light matrix, are elongated, vesicular, or branched in appearance. In vitamin-deficient cells, numerous mitochondrial profiles are evident. They have a regular circular or ovoid appearance. The inner membranes are regularly arrayed in an electron-dense matrix and generally appear elongated. By means of partial 3-dimensional reconstruction of whole cells the appearance of mitochondrial profiles in vitamin-deficient cells can be explained by the increased branching of a single structure. Following transfer of vitamin-deficient cells to complete medium, normal mitochondrial structure is attained by ∼3 hr. Reduced-minus-oxidized difference spectra of suspensions of normal and vitamin-deficient cells, grown with gentle aeration, were recorded. The concentrations of a- and b-type cytochromes are reduced by 80-90%, and c-type cytochromes are reduced by 40% in thiamine-deficient cells.     

Metabolism of Anxiolytics and Hypnotics: Benzodiazepines, Buspirone, Zoplicone, and Zolpidem

1. The benzodiazepines are among the most frequently prescribed of all drugs and have been used for their anxiolytic, anticonvulsant, and sedative/hypnotic properties. Since absorption rates, volumes of distribution, and elimination rates differ greatly among the benzodiazepine derivatives, each benzodiazepine has a unique plasma concentration curve. Although the time to peak plasma levels provides a rough guide, it is not equivalent to the time to clinical onset of effect. The importance of and half-lives in the actions of benzodiazepines is discussed.2. The role of cytochrome P450 isozymes in the metabolism of benzodiazepines and in potential pharmacokinetic interactions between the benzodiazepines and other coadministered drugs is discussed.3. Buspirone, an anxiolytic with minimal sedative effects, undergoes extensive metabolism, with hydroxylation and dealkylation being the major pathways. Pharmacokinetic interactions of buspirone with other coadministered drugs seem to be minimal.4. Zopiclone and zolpidem are used primarily as hypnotics. Both are extensively metabolized; N-demethylation, N-oxidation, and decarboxylation of zopiclone occur, and zolpidem undergoes oxidation of methyl groups and hydroxylation of a position on the imidazolepyridine ring system. Zopiclone has a chiral centre, and demonstrates stereoselective pharmacokinetics. Metabolic drug–drug interactions have been reported with zopiclone and erythromycin, trimipramine, and carbamazepine. Reports to date indicate minimal interactions of zolpidem with coadministered drugs; however, it has been reported to affect the C _max and clearance of chlorpromazepine and to decrease metabolism of the antiviral agent ritonavin. Since CYP3A4 has been reported to play an important role in metabolism of zolpidem, possible interactions with drugs which are substrates and/or inhibitors of that CYP isozyme should be considered.