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PubMed1981

Uptake of thallous ions by mitochondria is stimulated by nonactin but not by respiration alone.

Nonrespiring rat-liver mitochondria swell in media containing high concentrations of thallous nitrate, indicating passive penetration of Tl+. This swelling could be further stimulated by 10 nM or more nonactin while even 1 microM valinomycin was without effect. Nonactin was also much more potent than valinomycin in stimulating swelling of respiring mitochondria in the presence of thallous acetate. It is evident that nonactin acts as a potent ionophore of Tl+ able to promote both the passive and energized uptake of Tl+ in mitochondria. The distribution of Tl+, present in trace concentrations below 1 mM, was measured during energisation by respiration both in the presence and absence of ionophores. Respiration induced net uptake of Tl+ only in the presence of ionophores, though Tl+ as a permeant cation was expected to sense respiration-induced changes in the membrane potential. The data may be interpreted as indicating that no transmembrane potential is formed upon energisation, but localized fields, which are able to interact with the lipophilic ionophore complexes of Tl+, but not with the hydrophilic cation Tl+. This interpretation is valid only if thermodynamic equilibrium has been reached.

Animals↗
PubMed1992

Characterisation of the control of respiration in potato tuber mitochondria using the top-down approach of metabolic control analysis.

Control over oxidative phosphorylation by purified potato mitochondria was determined using the top-down approach of metabolic control analysis. The control over the respiration rate, phosphorylation rate, proton-leak rate and proton motive force exerted by the respiratory chain, phosphorylation reactions and the proton leak were measured over a range of phosphorylation rates from resting (state 4) to maximal (state 3). These rates were obtained by adding different amounts of hexokinase in the presence of glucose, or different amounts of oligomycin in the presence of ADP. The respiratory substrate was NADH or succinate, both of which feed electrons directly to ubiquinone. The rate of oxygen consumption by the alternative oxidase pathway was negligible with NADH as substrate but was measurable with succinate and was subtracted. Control over the respiration rate in potato mitochondria was predominantly exerted by the respiratory chain at all rates except close to state 4, where control by the proton leak was equally or more important. For oxidation of NADH, the flux control coefficient over the respiration rate exerted by the respiratory chain in state 3 was between 0.8 and 1.0, while in state 4, control over the respiration rate was shared about equally between the chain and the proton leak. The control over the phosphorylation rate was predominantly exerted by the respiratory chain, although at low rates control by the phosphorylation system was also important. For oxidation of NADH, the flux control coefficient over the phosphorylation rate exerted by the respiratory chain in state 3 was 0.8-1.0, while near state 4 the flux control coefficients over the phosphorylation rate were about 0.8 for the phosphorylation system and 0.25 for the chain. Control over the proton leak rate was shared between the respiratory chain and the proton leak; the phosphorylation system had negative control. For oxidation of NADH, the flux control coefficients over the leak rate in state 3 were 1.0 for the leak, 0.4 for the chain and -0.4 for the phosphorylation system, while in state 4 the flux control coefficients over leak rate were about 0.5 for the leak and 0.5 for the chain. Control over the magnitude of the protonmotive force was small, between -0.2 and +0.2, reflecting the way the system operates to keep the protonmotive force fairly constant; the respiratory chain and the phosphorylation system had equal and opposite control and there was very little control by the proton leak except near state 4.

Hydrogen-Ion Concentration↗
PubMed1996

Striking differences between the kinetics of regulation of respiration by ADP in slow-twitch and fast-twitch muscles in vivo.

The kinetics of in vivo regulation of mitochondrial respiration by ADP was studied in rat heart, slow-twitch skeletal muscle (soleus) and fast-twitch skeletal muscle (gastrocnemius, plantaris, quadriceps and tibialis anterior) by means of saponin-skinned fibres. Mitochondrial respiratory parameters were determined in the absence and presence of creatine (20 mM), and the effect of proteolytic enzymes (trypsin, chymotrypsin or elastase) on these parameters was investigated in detail. The results of these experiments confirm the observation of Veksler et al. [Veksler, V.I., Kuznetsov, A. V., Anflous, K., Mateo, P., van Deursen, J., Wieringa, B. & Ventura-Clapier, R. (1995) J. Biol. Chem. 270, 19921-19929], who studied muscle fibres from normal and transgenic mice, that the kinetics of respiration regulation in muscle cells is tissue specific. We found that in rat cardiac and soleus muscle fibres the apparent K(m) for respiration regulation was 300-400 microM and decreased to 50-80 microM in the presence of creatine. In contrast, in skinned fibres from gastrocnemius, plantaris, tibialis anterior and quadriceps muscles, this value was initially very low, 10-20 microM, i.e. the same as that is in isolated muscle mitochondria, and the effect of creatine was not observable under these experimental conditions. Treatment of the fibres with trypsin, chymotrypsin or elastase (0.125 micrograms/ml) for 15 min decreased the apparent K(m) for ADP in cardiac and soleus muscle fibres to 40-98 microM without significant alteration of Vmax or the intactness of outer mitochondrial membrane, as assessed by the cytochrome c test. In fibres from gastrocnemius, trypsin increased the apparent K(m) for ADP transiently. The effects of trypsin and chymotrypsin were studied in detail and found to be concentration dependent and time dependent. The effects were characterised by saturation phenomenon with respect to the proteolytic enzyme concentration, saturation being observed above 1 microM enzyme. These results are taken to show that in cardiac and slow-twitch skeletal muscle, the permeability of the outer mitochondrial membrane to adenine nucleotides is low and controlled by a cytoplasmic protein that is sensitive to trypsin and chymotrypsin. This protein may participate in feedback signal transduction by a mechanism of vectorial-ligand conduction. This protein factor is not expressed in fast-twitch skeletal muscle, in which cellular mechanism of regulation of respiration is probably very different from that of slow-twitch muscles.

Adenosine Diphosphate↗
PubMed2005

Large daily variation in 13C-enrichment of leaf-respired CO2 in two Quercus forest canopies.

The use of the 13C : 12C isotopic ratio (delta13C) of leaf-respired CO2 to trace carbon fluxes in plants and ecosystems is limited by little information on temporal variations in delta13C of leaf dark-respired CO2 (delta13Cr) under field conditions. Here, we explored variability in delta13Cr and its relationship to key respiratory substrates from collections of leaf dark-respired CO2, carbohydrate extractions and gas exchange measurements over 24-h periods in two Quercus canopies. Throughout both canopies, delta13Cr became progressively 13C-enriched during the photoperiod, by up to 7%, then 13C-depleted at night relative to the photoperiod. This cycle could not be reconciled with delta13C of soluble sugars (delta13Css), starch (delta13Cst), lipids (delta13Cl), cellulose (delta13Cc) or with calculated photosynthetic discrimination (Delta). However, photoperiod progressive enrichment in delta13Cr was correlated with cumulative carbon assimilation (r2 = 0.91). We concluded that there is considerable short-term variation in delta13Cr in forest canopies, that it is consistent with current hypotheses for 13C fractionation during leaf respiration, that leaf carbohydrates cannot be used as surrogates for delta13Cr, and that diel changes in leaf carbohydrate status could be used to predict changes in delta13Cr empirically.

Carbon Dioxide↗
PubMed1991

Selective impairment of respiration in mitochondria isolated from brain subregions following transient forebrain ischemia in the rat.

Using Percoll density gradient centrifugation, free (nonsynaptosomal) mitochondria were isolated from the dorsal-lateral striatum and paramedian neocortex of rats during complete forebrain ischemia and reperfusion. Mitochondria prepared from either region after 30 min of ischemia showed decreased state 3 (ADP and substrate present) and uncoupled respiration rates (19-45% reductions) with pyruvate plus malate as substrates, whereas state 4 respiration (no ADP present) was preserved. At 6 h of recirculation, state 3 and uncoupled respiration rates for mitochondria from the paramedian neocortex (a region resistant to ischemic damage) were similar to or even increased compared with control values. By contrast, in mitochondria from the dorsal-lateral striatum (a region containing neurons susceptible to global ischemia), decreases in state 3 and uncoupled respiration rates (25 and 30% less than control values) were again observed after 6 h of recirculation. With succinate as respiratory substrate, however, no significant differences from control values were found in either region at this time point. By 24 h of recirculation, respiratory activity with either pyruvate plus malate or succinate was greatly reduced in samples from the dorsal-lateral striatum, probably reflecting complete loss of function in some organelles. In contrast with these marked changes in free mitochondria, the respiratory properties of synaptosomal mitochondria, assessed from measurements in unfractionated homogenates, were unchanged from controls in the dorsal-lateral striatum at each of the time points studied, but showed reductions (19-22%) during ischemia and after 24 h of recirculation in the paramedian neocortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2000

Competition between methanogenesis and quinone respiration for ecologically important substrates in anaerobic consortia.

Anaerobic consortia obtained from a wide variety of environments were tested for oxidizing several ecologically significant substrates with the humic model compound, anthraquinone-2,6-disulfonate (AQDS), as terminal electron acceptor. All the substrates, including hydrogen, acetate, propionate, methanol and lactate, were completely or partially converted to methane when bicarbonate was the only electron acceptor available. Addition of AQDS (20 mM) to the cultures prevented methanogenesis in most cases and AQDS reduction became the preferred pathway. AQDS was shown to be toxic for methanogenesis and this effect played an important role in enabling quinone-respiring bacteria to outcompete methanogens. Furthermore, AQDS respiration is thermodynamically more favorable than methanogenesis. All the consortia evaluated were capable of oxidizing hydrogen linked to the reduction of AQDS. Most inocula tested were also able to oxidize acetate and lactate in the same way. When methanol was provided as an electron donor competition between methanogenesis and acetogenesis occurred. Acetate accumulated from the latter process was responsible for quinone respiration. These results suggest that quinone-respiring bacteria are ubiquitous and that quinones in humus may significantly contribute to carbon cycling process by serving as a terminal electron acceptor for the anaerobic microbial oxidation of a wide variety of ecologically important substrates.

Journal Article↗
PubMed1981

Further studies on the gonadotrophin-induced inhibition of respiration in the preovulatory rat cumulus oophorus.

It has been shown earlier that LH decreases the oxygen consumption of the rat cumulus oophorus cells, i.e. the granulosa cells immediately surrounding the follicular oocyte. The decrease occurs in the preovulatory period at the time when the oocyte resumes and completes meiosis. This study examines in more detail the time-course of LH-induced inhibition of cumulus respiration. The results show that when isolated cumuli were exposed to LH during in vitro culture a significant inhibition of respiration occurred within one hour. When follicle-enclosed cumuli were exposed to LH, in vivo or in vitro, the decrease in respiration was not evident until 4 hours after the hormone exposure. By this time oocyte maturation was already in progress. The results suggest that the decrease in cumulus respiration may not be directly linked to the onset of oocyte meiosis.

Animals↗
PubMed1967

The respiration of the anterior byssus retractor muscle of Mytilus edulis (ABRM) after a phasic contraction.

1. The oxygen consumption of isolated anterior byssus retractor muscle of Mytilus edulis (ABRM) has been measured at rest and after phasic contractions induced by a.c. stimulation.2. The respiration was measured with a Clark oxygen electrode in successive periods of 5 or 15 min, at 20 degrees C.3. The resting respiration is 71.8 +/- 2.4 n-moles O(2)/g wet weight.min (mean +/- S.E., n = 70). It is increased by a release and decreased by a passive stretch.4. After phasic stimulation of up to 30 sec the respiration is increased and returns to a slightly higher level than the resting level in an exponential fashion with a time constant of about 10 min.5. The duration of stimulation does not change the time course of the excess respiration but it affects its magnitude. The amount of extra oxygen consumed, in n-moles O(2)/g, is made up of a constant amount, 449 +/- 102, and an amount that depends on the duration of stimulation (t, sec), which is given by t x 13.2 +/- 4.3. When due account is taken for the tension developed, these parameters become 83.1 +/- 20.7 and t x 1.24 +/- 0.66 n-moles O(2)/g muscle and kg/cm(2) of tension. This regression analysis is based on forty-eight data, with a residual error based on 5 degrees of freedom.6. Release of the tension after the last stimulus of a 30 sec tetanus reduces by half the extra oxygen consumed during the recovery whereas the same release applied 5 min later has a much smaller effect. This suggests that relaxation is an active process.7. From these measurements of the recovery metabolism the energy cost of the contraction was estimated and compared with this cost in vertebrate striated muscle. The constant item has about the same magnitude, but the item related to the duration of stimulation is about 250 times smaller.

Animals↗
PubMed1970

The effect on respiration of abrupt changes in carotid artery pH and PCO2 in the cat.

1. An in vivo pH monitoring technique was used to assess changes in pH, and by inference changes in P(CO2), in the carotid artery of anaesthetized cats. The changes in carotid artery pH and respiration following abrupt injections of various acids into the carotid artery or aorta were investigated.2. Injections of saline equilibrated with 100% CO(2), timed to produce changes at the carotid body chemoreceptors during early inspiration caused an increase in the tidal volume of that breath. The amplitude and rate of change of the pH changes so produced were comparable with those of the oscillations in pH produced by respiration itself.3. The respiratory responses to injection of saline equilibrated with 100% CO(2) occurred whether the animal was breathing air or 100% O(2).4. Injections of lactic or hydrochloric acid were without an effect on respiration, except when pH changes larger than 0.1 pH unit were produced. A NaHCO(3) solution equilibrated with 30% CO(2) stimulated respiration, even though the solution was alkaline to the cat's arterial blood and induced an alkaline change in arterial pH.5. Infiltration of the carotid sinus nerve area with procaine temporarily abolished the respiratory response to injections of saline equilibrated with 100% CO(2).

Animals↗
PubMed2006

Phased attenuation correction in respiration correlated computed tomography/positron emitted tomography.

The motion of lung tumors with respiration causes difficulties in the imaging with computed tomography (CT) and positronemitted tomography (PET). Since an accurate knowledge of the position of the tumor and the surrounding tissues is needed for radiation treatment planning, it is important to improve CT/PET image acquisition. The purpose of this study was to evaluate the potential to improve image acquisition using phased attenuation correction in respiration correlated CT/PET, where data of both modalities were binned retrospectively. Respiration correlated scans were made on a Siemens Biograph Sensation 16 CT/PET scanner which was modified to make a low pitch CT scan and list mode PET scan possible. A lollipop phantom was used in the experiments. The sphere with a diameter of 3.1 cm was filled with approximately 20 MBq 18F-FDG. Three longitudinal movement amplitudes were tested: 2.5, 3.9, and 4.8 cm. After collection of the raw CT data, list mode PET data, and the respiratory signal CT/PET images were binned to ten phases with the help of in-house-built software. Each PET phase was corrected for attenuation with CT data of the corresponding phase. For comparison, the attenuation correction was also performed with nonrespiration correlated (non-RC) CT data. The volume and the amplitude of the movement were calculated for every phaseof both the CT and PET data (with phased attenuation correction). Maximum and average activity concentrations were compared between the phased and nonphased attenuation corrected PET. With a standard non-RC CT/PET scan, the volume was underestimated by as much as 46% in CT and the PET volume was overestimated to 370%. The volumes found with RC-CT/PET scanning had average deviations of 1.9% (+/- 4.8%) and 1.5% (+/- 3.4%) from the actual volume, for the CT and PET volumes, respectively. Evaluation of the maximum activity concentration showed a clear displacement in the images with non-RC attenuation correction, and activity values were on average14% (+/- 12%) lower than with phased attenuation correction. The standard deviation of the maximum activity values found in the different phases was a factor of 10 smaller when phased attenuation correction was applied. In this phantom study, we have shown that a combination of respiration correlated CT/PET scanning with application of phased attenuation correction can improve the imaging of moving objects and can lead to improved volume estimation and a more precise localization and quantification of the activity.

Humans↗
PubMed2004

arrA is a reliable marker for As(V) respiration.

Arsenate [As(V)]-respiring bacteria affect the speciation and mobilization of arsenic in the environment. This can lead to arsenic contamination of drinking water supplies and deleterious consequences for human health. Using molecular genetics, we show that the functional gene for As(V) respiration, arrA, is highly conserved; that it is required for As(V) reduction to arsenite when arsenic is sorbed onto iron minerals; and that it can be used to identify the presence and activity of As(V)-respiring bacteria in arsenic-contaminated iron-rich sediments. The expression of arrA thus can be used to monitor sites in which As(V)-respiring bacteria may be controlling arsenic geochemistry.

Archaea↗
PubMed2003

Relationships between respiration and susceptibility to azole antifungals in Candida glabrata.

Over the past two decades, the incidence of infections due to Candida glabrata, a yeast with intrinsic low susceptibility to azole antifungals, has increased markedly. Respiratory deficiency due to mutations in mitochondrial DNA (mtDNA) associated with resistance to azoles frequently occurs in vitro in this species. In order to specify the relationships between respiration and azole susceptibility, the effects of respiratory chain inhibitors on a wild-type isolate of C. glabrata were evaluated. Respiration of blastoconidia was immediately blocked after extemporaneous addition of potassium cyanide, whereas a 4-h preincubation was required for sodium azide. Antifungal susceptibility determined by a disk diffusion method on Casitone agar containing sodium azide showed a significant decrease in the susceptibility to azoles. Biweekly subculturing on Casitone agar supplemented with sodium azide was therefore performed. This resulted after 40 passages in the isolation of a respiration-deficient mutant, as suggested by its lack of growth on glycerol-containing agar. This respiratory deficiency was confirmed by flow cytometric analysis of blastoconidia stained with rhodamine 123 and by oxygraphy. Moreover, transmission electron microscopy and restriction endonuclease analysis of the mtDNA of mutant cells demonstrated the mitochondrial origin of the respiratory deficiency. Finally, this mutant exhibited cross-resistance to all the azoles tested. In conclusion, blockage of respiration in C. glabrata induces decreased susceptibility to azoles, culminating in azole resistance due to the deletion of mtDNA. This mechanism could explain the induction of petite mutations by azole antifungals which have been demonstrated to act directly on the mitochondrial respiratory chain.

Antifungal Agents↗
PubMed2006

Anaerobic respiration on tellurate and other metalloids in bacteria from hydrothermal vent fields in the eastern Pacific Ocean.

This paper reports the discovery of anaerobic respiration on tellurate by bacteria isolated from deep ocean (1,543 to 1,791 m) hydrothermal vent worms. The first evidence for selenite- and vanadate-respiring bacteria from deep ocean hydrothermal vents is also presented. Enumeration of the anaerobic metal(loid)-resistant microbial community associated with hydrothermal vent animals indicates that a greater proportion of the bacterial community associated with certain vent fauna resists and reduces metal(loid)s anaerobically than aerobically, suggesting that anaerobic metal(loid) respiration might be an important process in bacteria that are symbiotic with vent fauna. Isolates from Axial Volcano and Explorer Ridge were tested for their ability to reduce tellurate, selenite, metavanadate, or orthovanadate in the absence of alternate electron acceptors. In the presence of metal(loid)s, strains showed an ability to grow and produce ATP, whereas in the absence of metal(loid)s, no growth or ATP production was observed. The protonophore carbonyl cyanide m-chlorophenylhydrazone depressed metal(loid) reduction. Anaerobic tellurate respiration will be a significant component in describing biogeochemical cycling of Te at hydrothermal vents.

Anaerobiosis↗
PubMed1986

Adhesion of the clay minerals montmorillonite, kaolinite, and attapulgite reduces respiration of Histoplasma capsulatum.

The respiration of three phenotypes of Histoplasma capsulatum, the causal agent of histoplasmosis in humans, was markedly reduced by low concentrations of montmorillonite but was reduced less by even higher concentrations of kaolinite or attapulgite (palygorskite). The reduction in respiration followed a pattern that suggested saturation-type kinetics: an initial sharp reduction that occurred with low concentrations of clay (0.01 to 0.5% [wt/vol]), followed by a more gradual reduction with higher concentrations (1 to 8%). Increases in viscosity (which could impair the movement of O2) caused by the clays were not responsible for the reduction in respiration, and the clays did not interfere with the availability of nutrients. Scanning electron microscopy after extensive washing showed that the clay particles were tightly bound to the hyphae, suggesting that the clays reduced the rate of respiration of H. capsulatum by adhering to the mycelial surface and, thereby, interfered with the movement of nutrients, metabolites, and gases across the mycelial wall.

Adhesiveness↗
PubMed1993

Use of 5-cyano-2,3-ditolyl tetrazolium chloride for quantifying planktonic and sessile respiring bacteria in drinking water.

Direct microscopic quantification of respiring (i.e., viable) bacteria was performed for drinking water samples and biofilms grown on different opaque substrata. Water samples or biofilms developed in flowing drinking water were incubated with the vital redox dye 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) and R2A medium. One hour of incubation with 0.5 mM CTC was sufficient to obtain intracellular reduction of CTC to the insoluble fluorescent formazan (CTF) product, which was indicative of cellular respiratory (i.e., electron transport) activity. This result was obtained with both planktonic and biofilm-associated cells. Planktonic bacteria were captured on 0.2-microns-pore-size polycarbonate membrane filters and examined by epifluorescence microscopy. Respiring cells containing CTF deposits were readily detected and quantified as red-fluorescing objects on a dark background. The number of CTC-reducing bacteria was consistently greater than the number of aerobic CFU determined on R2A medium. Approximately 1 to 10% of the total planktonic population (determined by counterstaining with 4,6-diamidino-2-phenylindole) were respirometrically active. The proportion of respiring bacteria in biofilms composed of drinking water microflora was greater, ranging from about 5 to 35%, depending on the substratum. Respiring cells were distributed more or less evenly in biofilms, as demonstrated by counterstaining with 4,6-diamidino-2-phenylindole. The amount of CTF deposited in single cells of Pseudomonas putida that formed monospecies biofilms was quantified by digital image analysis and used to indicate cumulative respiratory activity. These data indicated significant cell-to-cell variation in respiratory activity and reduced electron transport following a brief period of nutrient starvation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2002

Microbial iron respiration can protect steel from corrosion.

Microbiologically influenced corrosion (MC) of steel has been attributed to the activity of biofilms that include anaerobic microorganisms such as iron-respiring bacteria, yet the mechanisms by which these organisms influence corrosion have been unclear. To study this process, we generated mutants of the iron-respiring bacterium Shewanella oneidensis strain MR-1 that were defective in biofilm formation and/or iron reduction. Electrochemical impedance spectroscopy was used to determine changes in the corrosion rate and corrosion potential as a function of time for these mutants in comparison to the wild type. Counter to prevailing theories of MC, our results indicate that biofilms comprising iron-respiring bacteria may reduce rather than accelerate the corrosion rate of steel. Corrosion inhibition appears to be due to reduction of ferric ions to ferrous ions and increased consumption of oxygen, both of which are direct consequences of microbial respiration.

Biofilms↗
PubMed2007

The cymA gene, encoding a tetraheme c-type cytochrome, is required for arsenate respiration in Shewanella species.

In Shewanella sp. strain ANA-3, utilization of arsenate as a terminal electron acceptor is conferred by a two-gene operon, arrAB, which lacks a gene encoding a membrane-anchoring subunit for the soluble ArrAB protein complex. Analysis of the genome sequence of Shewanella putrefaciens strain CN-32 showed that it also contained the same arrAB operon with 100% nucleotide identity. Here, we report that CN-32 respires arsenate and that this metabolism is dependent on arrA and an additional gene encoding a membrane-associated tetraheme c-type cytochrome, cymA. Deletion of cymA in ANA-3 also eliminated growth on and reduction of arsenate. The DeltacymA strains of CN-32 and ANA-3 negatively affected the reduction of Fe(III) and Mn(IV) but not growth on nitrate. Unlike the CN-32 DeltacymA strain, growth on fumarate was absent in the DeltacymA strain of ANA-3. Both homologous and heterologous complementation of cymA in trans restored growth on arsenate in DeltacymA strains of both CN-32 and ANA-3. Transcription patterns of cymA showed that it was induced under anaerobic conditions in the presence of fumarate and arsenate. Nitrate-grown cells exhibited the greatest level of cymA expression in both wild-type strains. Lastly, site-directed mutagenesis of the first Cys to Ser in each of the four CXXCH c-heme binding motifs of the CN-32 CymA nearly eliminated growth on and reduction of arsenate. Together, these results indicate that the biochemical mechanism of arsenate respiration and reduction requires the interactions of ArrAB with a membrane-associated tetraheme cytochrome, which in the non-arsenate-respiring Shewanella species Shewanella oneidensis strain MR-1, has pleiotropic effects on Fe(III), Mn(IV), dimethyl sulfoxide, nitrate, nitrite, and fumarate respiration.

Amino Acid Sequence↗
PubMed1972

Development of respiration and mitochondria in Mucor genevensis after anaerobic growth: absence of glucose repression.

Respiration and mitochondria in Mucor genevensis, a facultatively anaerobic dimorphic mold, have been studied in aerobically and anaerobically grown cells and in anaerobically grown cells adapting to aerobic conditions. Respiration in hyphae continues at a high level during aerobic growth but drops rapidly on exhaustion of glucose. In anaerobically grown yeastlike cells, containing no recognizable aerobic cytochromes, a small cyanide-insensitive respiration occurs. Mitochondria with well defined cristae are visible in negative contrast after KMnO(4) fixation of stringently anaerobic cells containing low amounts of fatty acid of which 10% or less are unsaturated. On aeration of anaerobically grown cells, respiratory capacity and cytochromes develop rapidly, even in the presence of 10% glucose, indicating that glucose does not repress development of respiration. However, mycelium formation by adapting yeastlike cells is repressed by high glucose concentration. In adapting cells, apparent changes in mitochondrial ultrastructure appear to be more related to changes in fixation properties of cells than to changes in the structure of mitochondria.

Aerobiosis↗