The antimycin-A-insensitive respiratory pathway of Candida parapsilosis: evidence for a second quinone involved specifically in its functioning

Xylose and yeasts: A story beyond xylitol production

Six different yeasts were used to study their metabolism of glucose and xylose, and mainly their capacity to produce ethanol and xylitol. The strains used were Candida guilliermondii, Debaryomyces hansenii, Saccharomyces cerevisiae, Kluyveromyces marxianus, Meyerozyma guilliermondii and Clavispora lusitaniae, four isolated from a rural mezcal fermentation facility. All of them produced ethanol when the substrate was glucose. When incubated in a medium containing xylose instead of glucose, only K. marxianus and M. guilliermondii were able to produce ethanol from xylose. On the other hand, all of them could produce some xylitol from xylose, but the most active in this regard were K. marxianus, M. guilliermondii, Candida lusitaniae, and C. guilliermondii with the highest amount of xylitol produced. The capacity of all strains to take up glucose and xylose was also studied. Xylose, in different degrees, produced a redox imbalance in all yeasts. Respiration capacity was also studied with glucose or xylose, where C. guilliermondii, D. hansenii, K. marxianus and M. guilliermondii showed higher cyanide resistant respiration when grown in xylose. Neither xylose transport nor xylitol production were enhanced by an acidic environment (pH 4), which can be interpreted as the absence of a proton/sugar symporter mechanism for xylose transport, except for C. lusitaniae. The effects produced by xylose and their magnitude depend on the background of the studied yeast and the conditions in which these are studied.

Intracardiac light catheter for rapid scanning transmural absorbance spectroscopy of perfused myocardium: measurement of myoglobin oxygenation and mitochondria redox state

Absorbance spectroscopy of intrinsic cardiac chromophores provides nondestructive assessment of cytosolic oxygenation and mitochondria redox state. Isolated perfused heart spectroscopy is usually conducted by collecting reflected light from the heart surface, which represents a combination of surface scattering events and light that traversed portions of the myocardium. Reflectance spectroscopy with complex surface scattering effects in the beating heart leads to difficulty in quantitating chromophore absorbance. In this study, surface scattering was minimized and transmural path length optimized by placing a light source within the left ventricular chamber while monitoring transmurally transmitted light at the epicardial surface. The custom-designed intrachamber light catheter was a flexible coaxial cable (2.42-Fr) terminated with an encapsulated side-firing LED of 1.8 × 0.8 mm, altogether similar in size to a Millar pressure catheter. The LED catheter had minimal impact on aortic flow and heart rate in Langendorff perfusion and did not impact stability of the left ventricule of the working heart. Changes in transmural absorbance spectra were deconvoluted using a library of chromophore reference spectra to quantify the relative contribution of specific chromophores to the changes in measured absorbance. This broad-band spectral deconvolution approach eliminated errors that may result from simple dual-wavelength absorbance intensity. The myoglobin oxygenation level was only 82.2 ± 3.0%, whereas cytochrome c and cytochrome a + a₃ were 13.3 ± 1.4% and 12.6 ± 2.2% reduced, respectively, in the Langendorff-perfused heart. The intracardiac illumination strategy permits transmural optical absorbance spectroscopy in perfused hearts, which provides a noninvasive real-time monitor of cytosolic oxygenation and mitochondria redox state.NEW & NOTEWORTHY Here, a novel nondestructive real-time approach for monitoring intrinsic indicators of cardiac metabolism and oxygenation is described using a catheter-based transillumination of the left ventricular free wall together with complete spectral analysis of transmitted light. This approach is a significant improvement in the quality of cardiac optical absorbance spectroscopic metabolic analyses.

Enzymatic dysfunction of mitochondrial complex I of the Candida albicans goa1 mutant is associated with increased reactive oxidants and cell death

We have previously shown that deletion of GOA1 (growth and oxidant adaptation) of Candida albicans results in a loss of mitochondrial membrane potential, ATP synthesis, increased sensitivity to oxidants and killing by human neutrophils, and avirulence in a systemic model of candidiasis. We established that translocation of Goa1p to mitochondria occurred during peroxide stress. In this report, we show that the goa1Δ (GOA31), compared to the wild type (WT) and a gene-reconstituted (GOA32) strain, exhibits sensitivity to inhibitors of the classical respiratory chain (CRC), including especially rotenone (complex I [CI]) and salicylhydroxamic acid (SHAM), an inhibitor of the alternative oxidase pathway (AOX), while potassium cyanide (KCN; CIV) causes a partial inhibition of respiration. In the presence of SHAM, however, GOA31 has an enhanced respiration, which we attribute to the parallel respiratory (PAR) pathway and alternative NADH dehydrogenases. Interestingly, deletion of GOA1 also results in a decrease in transcription of the alternative oxidase gene AOX1 in untreated cells as well as negligible AOX1 and AOX2 transcription in peroxide-treated cells. To explain the rotenone sensitivity, we measured enzyme activities of complexes I to IV (CI to CIV) and observed a major loss of CI activity in GOA31 but not in control strains. Enzymatic data of CI were supported by blue native polyacrylamide gel electrophoresis (BN-PAGE) experiments which demonstrated less CI protein and reduced enzyme activity. The consequence of a defective CI in GOA31 is an increase in reactive oxidant species (ROS), loss of chronological aging, and programmed cell death ([PCD] apoptosis) in vitro compared to control strains. The increase in PCD was indicated by an increase in caspase activity and DNA fragmentation in GOA31. Thus, GOA1 is required for a functional CI and partially for the AOX pathway; loss of GOA1 compromises cell survival. Further, the loss of chronological aging is new to studies of Candida species and may offer an insight into therapies to control these pathogens. Our observation of increased ROS production associated with a defective CI and PCD is reminiscent of mitochondrial studies of patients with some types of neurodegenerative diseases where CI and/or CIII dysfunctions lead to increased ROS and apoptosis.

Respiration, oxidative phosphorylation, and uncoupling protein in Candida albicans

The respiration, membrane potential (Deltapsi), and oxidative phosphorylation of mitochondria in situ were determined in spheroplasts obtained from Candida albicans control strain ATCC 90028 by lyticase treatment. Mitochondria in situ were able to phosphorylate externally added ADP (200 microM) in the presence of 0.05% BSA. Mitochondria in situ generated and sustained stable mitochondrial Deltapsi respiring on 5 mM NAD-linked substrates, 5 mM succinate, or 100 microM N,N,N',N'-tetramethyl-p-phenylenediamine dihydrochloride plus 1 mM ascorbate. Rotenone (4 microM) inhibited respiration by 30% and 2 micro M antimycin A or myxothiazole and 1 mM cyanide inhibited it by 85%. Cyanide-insensitive respiration was partially blocked by 2 mM benzohydroxamic acid, suggesting the presence of an alternative oxidase. Candida albicans mitochondria in situ presented a carboxyatractyloside-insensitive increase of Deltapsi induced by 5 mM ATP and 0.5% BSA, and Deltapsi decrease induced by 10 microM linoleic acid, both suggesting the existence of an uncoupling protein. The presence of this protein was subsequently confirmed by immunodetection and respiration experiments with isolated mitochondria. In conclusion, Candida albicans ATCC 90028 possesses an alternative electron transfer chain and alternative oxidase, both absent in animal cells. These pathways can be exceptional targets for the design of new chemotherapeutic agents. Blockage of these respiratory pathways together with inhibition of the uncoupling protein (another potential target for drug design) could lead to increased production of reactive oxygen species, dysfunction of Candida mitochondria, and possibly to oxidative cell death.

Cyanide-resistant respiration is frequent, but confined to yeasts incapable of aerobic fermentation

In Pichia membranifaciens, cyanide-resistant respiration (CRR) sensitive to salicylhydroxamic acid emerged after forced aeration of starved cells for 4 h. Surveying a large number of species by this simple methodology, we found that CRR is very frequent among yeasts. Remarkably, considering our results together with previous data in the literature, CRR was present in 24 out of 28 non-fermentative or Crabtree-negative yeasts and absent in 10 out of 12 Crabtree-positive yeasts. We submit that, as alternatives to cytochromic respiration, yeasts developed two strategies: either aerobic fermentation in Crabtree-positive yeasts or CRR in non-fermentative or Crabtree-negative yeasts.

Oxidative phosphorylation supported by an alternative respiratory pathway in mitochondria from Euglena

The effect of antimycin, myxothiazol, 2-heptyl-4-hydroxyquinoline-N-oxide, stigmatellin and cyanide on respiration, ATP synthesis, cytochrome c reductase, and membrane potential in mitochondria isolated from dark-grown Euglena cells was determined. With L-lactate as substrate, ATP synthesis was partially inhibited by antimycin, but the other four inhibitors completely abolished the process. Cyanide also inhibited the antimycin-resistant ATP synthesis. Membrane potential was collapsed (<60 mV) by cyanide and stigmatellin. However, in the presence of antimycin, a H(+)60 mV) that sufficed to drive ATP synthesis remained. Cytochrome c reductase, with L-lactate as donor, was diminished by antimycin and myxothiazol. Cytochrome bc(1) complex activity was fully inhibited by antimycin, but it was resistant to myxothiazol. Stigmatellin inhibited both L-lactate-dependent cytochrome c reductase and cytochrome bc(1) complex activities. Respiration was partially inhibited by the five inhibitors. The cyanide-resistant respiration was strongly inhibited by diphenylamine, n-propyl-gallate, salicylhydroxamic acid and disulfiram. Based on these results, a model of the respiratory chain of Euglena mitochondria is proposed, in which a quinol-cytochrome c oxidoreductase resistant to antimycin, and a quinol oxidase resistant to antimycin and cyanide are included.

Partitioning of electron flux between the respiratory chains of the yeast Candida parapsilosis: parallel working of the two chains

Partitioning of the electron flux between the classical and the alternative respiratory chains of the yeast Candida parapsilosis, was measured as a function of the oxidation rate and of the Q-pool redox poise. At low respiration rate, electrons from external NADH travelled preferentially through the alternative pathway as indicated by the antimycin A-insensitivity of electron flow. Inhibition of the alternative pathway by SHAM restored full antimycin A-sensitivity to the remaining electro flow. The dependence of the respiratory rate on the redox poise of the quinone pool was investigated when the electron flux was mediated either by the main respiratory chain (growth in the absence of antimycin A) or by the second respiratory chain (growth in the presence of antimycin A). In the former case, a linear relationship was found between these two parameters. In contrast, in the latter case, the relationship between Q-pool reduction level and electron flux was non-linear, but it could be resolved into two distinct curves. This second quinone is not reducible in the presence of antimycin A but only in the presence of high concentrations of myxothiazol or cyanide. Since two quinone species exist in C. parapsilosis, UQ9 and Qx (C33H54O4), we hypothesized that these two curves could correspond to the functioning of the second quinone engaged during the alternative pathway activity. Partitioning of electrons between both respiratory chains could occur upstream of complex III with the second chain functioning in parallel to the main one, and with the additional possibility of merging into the main one at the complex IV level.

Isolation, characterization and function of the two cytochromes c of the yeast Candida parapsilosis

Candida parapsilosis is a strictly aerobic yeast which possesses two respiratory chains with a peculiar organisation, different from that of plant mitochondria. Besides the classical electron transport pathway, mitochondria of C. parapsilosis develops an alternative pathway, which does not branch off at the ubiquinone level, but merges at the complex IV level. Two pools of cytochromes c were distinguished by their spectrometric and potentiometric properties: (i) sequential cytochrome c reduction was promoted by two substrates, PMS (Em = 70 mV) and TMPD (Em = 280 mV). TMPD promoted the reduction of a cytochrome c with maxima at 551.9 and 417.3 nm for the alpha and the Soret bands, respectively, whereas cytochrome c reducible by PMS exhibited maxima at 549.7 and 419.9 nm; (ii) two midpoint redox potentials were resolved at 180 mV and 280 mV, respectively. The two cytochromes c were copurified by ion-exchange chromatography on Amberlite; after this step, the two cytochromes c can always be differentiated by TMPD and PMS, these reductants promoting different absorption bands. The two cytochromes c were separated by reverse-phase HPLC; this last purification step resolved two proteins with the same relative molecular mass of 13600 but a different amino-acid composition. Comparison of N-terminal sequences revealed differences between the two proteins. It was hypothesized that one cytochrome c is implicated in the functioning of the main chain and the other in that of the secondary pathway.