Polarographic measurement of steady state kinetics of oxygen uptake by biochemical samples

The Broad-Spectrum Antimicrobial Potential of [Mn(CO)4(S2CNMe(CH2CO2H))], a Water-Soluble CO-Releasing Molecule (CORM-401): Intracellular Accumulation, Transcriptomic and Statistical Analyses, and Membrane Polarization

AIMS

Carbon monoxide (CO)-releasing molecules (CORMs) are candidates for animal and antimicrobial therapeutics. We aimed to probe the antimicrobial potential of a novel manganese CORM.

RESULTS

[Mn(CO)₄S₂CNMe(CH₂CO₂H)], CORM-401, inhibits growth of Escherichia coli and several antibiotic-resistant clinical pathogens. CORM-401 releases CO that binds oxidases in vivo, but is an ineffective respiratory inhibitor. Extensive CORM accumulation (assayed as intracellular manganese) accompanies antimicrobial activity. CORM-401 stimulates respiration, polarizes the cytoplasmic membrane in an uncoupler-like manner, and elicits loss of intracellular potassium and zinc. Transcriptomics and mathematical modeling of transcription factor activities reveal a multifaceted response characterized by elevated expression of genes encoding potassium uptake, efflux pumps, and envelope stress responses. Regulators implicated in stress responses (CpxR), respiration (Arc, Fnr), methionine biosynthesis (MetJ), and iron homeostasis (Fur) are significantly disturbed. Although CORM-401 reduces bacterial growth in combination with cefotaxime and trimethoprim, fractional inhibition studies reveal no interaction.

INNOVATION

We present the most detailed microbiological analysis yet of a CORM that is not a ruthenium carbonyl. We demonstrate CO-independent striking effects on the bacterial membrane and global transcriptomic responses.

CONCLUSIONS

CORM-401, contrary to our expectations of a CO delivery vehicle, does not inhibit respiration. It accumulates in the cytoplasm, acts like an uncoupler in disrupting cytoplasmic ion balance, and triggers multiple effects, including osmotic stress and futile respiration. Rebound Track: This work was rejected during standard peer review and rescued by rebound peer review (Antioxid Redox Signal 16: 293-296, 2012) with the following serving as open reviewers: Miguel Aon, Giancarlo Biagini, James Imlay, and Nigel Robinson. Antioxid. Redox Signal. 28, 1286-1308.

Antimicrobial Activity of the Manganese Photoactivated Carbon Monoxide-Releasing Molecule [Mn(CO)3(tpa-κ(3)N)](+) Against a Pathogenic Escherichia coli that Causes Urinary Infections

AIMS

We set out to investigate the antibacterial activity of a new Mn-based photoactivated carbon monoxide-releasing molecule (PhotoCORM, [Mn(CO)3(tpa-κ(3)N)](+)) against an antibiotic-resistant uropathogenic strain (EC958) of Escherichia coli.

RESULTS

Activated PhotoCORM inhibits growth and decreases viability of E. coli EC958, but non-illuminated carbon monoxide-releasing molecule (CORM) is without effect. NADH-supported respiration rates are significantly decreased by activated PhotoCORM, mimicking the effect of dissolved CO gas. CO from the PhotoCORM binds to intracellular targets, namely respiratory oxidases in strain EC958 and a bacterial globin heterologously expressed in strain K-12. However, unlike previously characterized CORMs, the PhotoCORM is not significantly accumulated in cells, as deduced from the cellular manganese content. Activated PhotoCORM reacts avidly with hydrogen peroxide producing hydroxyl radicals; the observed peroxide-enhanced toxicity of the PhotoCORM is ameliorated by thiourea. The PhotoCORM also potentiates the effect of the antibiotic, doxycycline.

INNOVATION

The present work investigates for the first time the antimicrobial activity of a light-activated PhotoCORM against an antibiotic-resistant pathogen. A comprehensive study of the effects of the PhotoCORM and its derivative molecules upon illumination is performed and mechanisms of toxicity of the activated PhotoCORM are investigated.

CONCLUSION

The PhotoCORM allows a site-specific and time-controlled release of CO in bacterial cultures and has the potential to provide much needed information on the generality of CORM activities in biology. Understanding the mechanism(s) of activated PhotoCORM toxicity will be key in exploring the potential of this and similar compounds as antimicrobial agents, perhaps in combinatorial therapies with other agents. Antioxid. Redox Signal. 24, 765-780.

Avoid Excessive Oxygen Levels in Experiments with Organisms, Tissues and Cells

O2 levels encountered in vivo in cells and tissues are almost always at least an order of magnitude less than atmospheric pO2 because of sensing, signalling and bioenergetic demand. Although deleterious reactions are minimized by protective mechanisms (residual toxic products scavenged and detoxified) ambient levels should be mimicked in experiments with whole organisms, their isolated organs, tissues or cells and also with cultures of cell lines. These are also important issues for microorganisms inhabiting low O2 niches within higher organisms and their cells. Here, we highlight the importance of optimization of micro-aerobic conditions for experimentation and the deleterious consequences of not doing so.

Ru(CO)3Cl(Glycinate) (CORM-3): a carbon monoxide-releasing molecule with broad-spectrum antimicrobial and photosensitive activities against respiration and cation transport in Escherichia coli

AIMS

Carbon monoxide (CO) delivered to cells and tissues by CO-releasing molecules (CO-RMs) has beneficial and toxic effects not mimicked by CO gas. The metal carbonyl Ru(CO)3Cl(glycinate) (CORM-3) is a novel, potent antimicrobial agent. Here, we established its mode of action.

RESULTS

CORM-3 inhibits respiration in several bacterial and yeast pathogens. In anoxic Escherichia coli suspensions, CORM-3 first stimulates, then inhibits respiration, but much higher concentrations of CORM-3 than of a classic protonophore are required for stimulation. Proton translocation measurements (H(+)/O quotients, i.e., H(+) extrusion on pulsing anaerobic cells with O2) show that respiratory stimulation cannot be attributed to true "uncoupling," that is, dissipation of the protonmotive force, or to direct stimulation of oxidase activity. Our data are consistent with CORM-3 facilitating the electrogenic transmembrane movement of K(+) (or Na(+)), causing a stimulation of respiration and H(+) pumping to compensate for the transient drop in membrane potential (ΔΨ). The effects on respiration are not mimicked by CO gas or control Ru compounds that do not release CO. Inhibition of respiration and loss of bacterial viability elicited by CORM-3 are reversible by white light, unambiguously identifying heme-containing oxidase(s) as target(s).

INNOVATION

This is the most complete study to date of the antimicrobial action of a CO-RM. Noteworthy are the demonstration of respiratory stimulation, electrogenic ion transport, and photosensitive activity, establishing terminal oxidases and ion transport as primary targets.

CONCLUSION

CORM-3 has multifaceted effects: increased membrane permeability, inhibition of terminal oxidases, and perhaps other unidentified mechanisms underlie its effectiveness in tackling microbial pathogenesis.

Direct measurements of steady-state kinetics of cyanobacterial n(2) uptake by membrane-leak mass spectrometry and comparisons between nitrogen fixation and acetylene reduction

A mass spectrometer with a membrane-covered inlet was used to measure nitrogen fixation by following changes in the concentration of dissolved N(2) in a stirred suspension of the cyanobacterium Anabaena variabilis in an open system. The results showed a good fit to Michaelis-Menten kinetics with a K(m) for N(2) of 65 muM at 35 degrees C, corresponding to 0.121 atmosphere of N(2). Corresponding values for the K(m) for acetylene reduction were 385 muM (0.011 atmosphere at 35 degrees C). Comparison of the values of V(max) for N(2) uptake with those for the acetylene reduction assay under similar conditions gave an average value of 3.8 for the conversion factor between N(2) and C(2)H(2) reduction. Reduction of protons to hydrogen was completely inhibited at sufficiently high concentrations of C(2)H(2), but even at saturating N(2) concentrations, 1 mol of H(2) was produced for every mole of N(2) reduced. This explains the finding that the observed C(2)H(2)/N(2) ratio is higher than the value of 3 expected from the requirement for two electrons for acetylene reduction and six for nitrogen reduction. The results correlate well with a mechanism for N(2) reduction involving the equation: N(2) + 8H + 8e --> 2NH(3) + H(2) which gives a conversion factor between C(2)H(2) and N(2) of 4. It is proposed that, in general, 4 is a more appropriate value than 3 for the conversion factor.

Carbohydrate and Amino Acid Fermentation in the Free-Living Primitive Protozoon Hexamita sp

Hexamita sp. is an amitochondriate free-living diplomonad which inhabits O(2)-limited environments, such as the deep waters and sediments of lakes and marine basins. C nuclear magnetic resonance spectroscopy reveals ethanol, lactate, acetate, and alanine as products of glucose fermentation under microaerobic conditions (23 to 34 muM O(2)). Propionic acid and butyric acid were also detected and are believed to be the result of fermentation of alternative substrates. Production of organic acids was greatest under microaerobic conditions (15 muM O(2)) and decreased under anaerobic (<0.25 muM O(2)) and aerobic (200 to 250 muM O(2)) conditions. Microaerobic incubation resulted in the production of high levels of oxidized end products (70% acetate) compared to that produced under anoxic conditions (20% acetate). In addition, data suggest that Hexamita cells contain the arginine dihydrolase pathway, generating energy from the catabolism of arginine to citrulline, ornithine, NH(4), and CO(2). The rate of arginine catabolism was higher under anoxic conditions than under microaerobic conditions. Hexamita cells were able to grow in the absence of a carbohydrate source, albeit with a lower growth rate and yield.

Oxygen uptake in cysts and trophozoites of Giardia lamblia

Oxygen uptake in cysts and trophozoites of the parasitic protozoan Giardia lamblia was examined. Both showed oxygen uptake activity, but that of cysts was only 10% to 20% that of trophozoites. Oxygen dependence of oxygen uptake in cysts and trophozoites showed oxygen maxima above which oxygen uptake decreased. The oxygen concentration at which the oxygen uptake rate was greatest was higher for trophozoites than for cysts. The effect of various inhibitors on cyst and trophozoite oxygen uptake suggested that flavoproteins and quinones play some role in oxygen uptake. The substrate specificities and the effect of inhibitors on G. lamblia trophozoites were similar to those observed for G. muris. Metronidazole, the drug most commonly used in treatment of giardiasis, inhibited oxygen uptake and motility in trophozoites; however, it had no obvious effect on either oxygen uptake or excystation in cysts. Menadione, a redox cycling naphthaquinone, first stimulated, then completely inhibited, oxygen uptake in cysts and trophozoites; a complete loss of cyst viability and trophozoite motility was also observed. The effect of menadione on G. lamblia may indicate that redox cycling compounds have potential as chemotherapeutic agents for the treatment of giardiasis.

The effects of oxygen on fermentation in Giardia lamblia

Detailed study of the effects of oxygen on the carbohydrate metabolism of Giardia lamblia revealed that low concentrations of oxygen (< 0.25 microM) produced profound alterations in the carbon balance of this organism. Although this concentration of oxygen could not be detected by mass spectrometry, a marked stimulation of ethanol production was observed. Associated with this was an inhibition of alanine production and oxidation of the intracellular NAD(P)H pool. Higher concentrations of oxygen inhibited ethanol production and further reduced levels of alanine. These results suggest that this stimulation is due to changes in carbon flux. Analysis of cell and medium hydrolysates after the growth of trophozoites in [U-14C]glucose suggests that G. lamblia does not synthesise detectable levels of labelled amino acids, except alanine and to a lesser extent valine, from this sugar. Trophozoites of G. lamblia have both glutamate dehydrogenase and alanine aminotransferase activity. As glutamate is taken up from the medium, it is suggested that glutamate dehydrogenase and alanine aminotransferase cooperate to convert pyruvate to alanine, with the concomitant oxidation of NAD(P)H.

Giardia lamblia produces alanine anaerobically but not in the presence of oxygen

Proton nuclear magnetic resonance was used to follow glucose metabolism in Giardia lamblia. Under strictly anaerobic conditions this organism produces equimolar ethanol and alanine as well as CO2 and some acetate. Aerobically the production of both alanine and ethanol are inhibited and more acetate and CO2 are formed. These changes in the balance of products are reversible over the range 0-46 microM O2. In the presence of 46 microM O2, alanine was not detectable. The O2-sensitivity of alanine production may highlight the necessity for redox-balancing reactions in an organism exposed in situ to fluctuating concentrations of O2.

Respiration in the filarial nematode Brugia pahangi

Glucose-supported O2 uptake in the filarial nematode Brugia pahangi was partially inhibited by antimycin A (30-40%), with the remaining activity being sensitive to o-hydroxydiphenyl or salicylhydroxamic acid (SHAM). The production of CO2 by B. pahangi in the presence of D-glucose was stimulated by O2; the stimulation of CO2; the stimulation of CO2 production was sensitive to antimycin A. The O2 dependencies of respiration showed that the apparent O2 affinity for B. pahangi was diminished in the presence of antimycin A; O2 thresholds for inhibition of respiration were observed which showed that the alternative electron transport pathway was less sensitive to inhibition at elevated O2 concentrations. H2O2 production and its excretion could be detected in whole B. pahangi; higher rates were observed in the presence of the uncoupler carbonyl cyanide m-chlorophenylhydrazone. The effects of inhibitors on H2O2 production suggest two sites of H2O2 production, one associated with the classical antimycin A-sensitive pathway, the other with the alternative respiratory pathway. The similarity in the O2 dependencies of H2O2 production and respiration may indicate that H2O2 production is involved in O2-mediated toxicity. Succinate and malate respiring sub-mitochondrial particles of B. pahangi produced O2.- radicals at a site on the antimycin A-sensitive respiratory pathway. Inhibition of the alternative electron pathway by SHAM was unusual; sub-millimolar concentrations markedly stimulated respiration, H2O2 production and O2.- production by 30, 20 and 25%, respectively, whereas higher concentrations (greater than 2.5 mM) inhibited respiration by 75% and H2O2 and O2.- production by up to 85%.

The O2-dependence of respiration and H2O2 production in the parasitic nematode Ascaridia galli

1. Respiration in the parasitic nematode worm Ascaridia galli was inhibited at O2 concentrations in excess of 255 microM, and an apparent Km,O2 of 174 microM was determined. 2. Mitochondria-enriched fractions isolated from the tissues of A. galli have much lower apparent Km,O2 values (approx. 5 microM). They produce H2O2 in the energized state; higher rates of H2O2 production were observed in the presence of the uncoupler carbonyl cyanide m-chlorophenylhydrazone. 3. Antimycin A inhibited respiration in muscle tissue mitochondria by 10%, but had no effect on respiration in gut + reproductive tissue mitochondria; the major portion of respiration in both types of mitochondria could be attributed to an alternative electron-transport pathway. 4. o-Hydroxydiphenyl, an inhibitor of alternative electron-transport pathways, inhibits respiration by 98% and completely inhibits the production of H2O2 in gut-plus-reproductive-tissue mitochondria; respiration and H2O2 production in muscle tissue mitochondria were inhibited by 90 and 86% respectively. 5. Another inhibitor of alternative electron transport, salicylhydroxamic acid, had the same effect as o-hydroxydiphenyl on H2O2 production and respiration in gut-plus-reproductive-tissue mitochondria. However, its effect on muscle tissue mitochondria was complex; a low concentration (0.35 mM) stimulated H2O2 production, whereas 3 mM inhibited respiration by 87% and prevented H2O2 production completely. 6. The similarities between the apparent Km,O2 values for H2O2 production and respiration in muscle mitochondria and in gut-plus-reproductive-tissue mitochondria suggests that the site of H2O2 production on the alternative electron-transport chain is cytochrome 'o'. 7. These results are discussed in relation to potential O2 toxicity in A. galli.

Hydrogen peroxide production in uncoupled mitochondria of the parasitic nematode worm Nippostrongylus brasiliensis

1. Mitochondria from the parasitic nematode worm Nippostrongylus brasiliensis produce H2O2 in the energized state; higher rates of H2O2 production were observed in the presence of the uncoupler carbonyl cyanide m-chlorophenylhydrazone. 2. Antimycin A inhibits respiration and H2O2 production by 70 and 65% respectively; the residual activities can be attributed to alternative electron-transport pathway(s). 3. o-Hydroxydiphenyl and 1,3,5-trihydroxybenzene, inhibitors of alternative electron transport, inhibit respiration by 37% and H2O2 production by 26%. 4. Another inhibitor of alternative electron transport, salicylhydroxamic acid, shows a complex mode of action; low concentrations (less than 0.5 mM) stimulate respiration and H2O2 production, whereas 2 mM-salicylhydroxamic acid inhibited respiration by 35% and stopped H2O2 production completely. 5. O2 thresholds were observed for the inhibition of respiration at O2 concentrations greater than 57.7 microM and inhibition of H2O2 production (greater than 20.5 microM-O2); apparent Km values for oxygen were 5.5 microM and 3.0 microM respectively. 6. In the presence of antimycin A the O2-inhibition thresholds and apparent Km values for O2 of respiration and H2O2 production matched closely, suggesting that the alternative oxidase is a likely site of H2O2 production. 7. These results are discussed in relation to O2 toxicity to N. brasiliensis.

Effects of inhibitors on the oxygen kinetics of Nippostrongylus brasiliensis

Endogenous respiration of the parasitic nematode Nippostrongylus brasiliensis and the succinate oxidase activity of isolated mitochondria were partially inhibited by antimycin A; the remaining respiratory activity was sensitive to salicylhydroxamic acid (SHAM). Sub-millimolar concentrations of SHAM markedly stimulated respiration by 60% in whole N. brasiliensis and isolated mitochondria; stimulation by SHAM was not observed in the presence of antimycin A. Little change in the relative fluxes of electrons through the classical, antimycin A-sensitive pathway and the alternative SHAM sensitive pathway was observed between low and high O2 concentrations; this may suggest that the O2 affinities of both pathways are similar. O2 dependence of respiration showed O2 thresholds above which respiration decreases; in the absence of inhibitors whole N. brasiliensis and isolated mitochondria had threshold values around 60 microM O2. Increased O2 threshold values were observed in the presence of SHAM and antimycin A. The apparent Km values for O2 of whole N. brasiliensis and isolated mitochondria were 31 +/- 2 microM O2 and 3.5 +/- 0.2 microM O2 respectively; this difference in apparent Km values may reflect the presence of O2 gradients in the whole worm. The Km and O2 inhibition threshold values observed for whole N. brasiliensis are in good agreement with the proposed range of O2 concentrations thought to exist within the worm's natural environment. H2O2 production was detected in respiring uncoupled mitochondria, but H2O2 could not be detected in the medium surrounding whole N. brasiliensis. SHAM-stimulated respiration was accompanied by increased H2O2 production which was prevented by the addition of antimycin A.

Metronidazole-resistant clinical isolates of Trichomonas vaginalis have lowered oxygen affinities

Oxygen affinities of metronidazole susceptible and resistant isolates of the parasitic flagellate protozoon Trichomonas vaginalis were determined by mass spectrometric methods. Apparent O2Km values for the respiration of non-proliferating cell suspensions were about 10-fold higher for metronidazole resistant strains than for the susceptible strains C1-NIH or NYH-286. Simultaneous monitoring of hydrogen evolution in the presence of increasing O2 tensions enabled apparent Ki values for H2 to be determined; and this function was independent of metronidazole susceptibility. Apparent O2 affinities of the hydrogenosomal and non-sedimentable fractions were determined for the strains CDC 85 (metronidazole resistant) and C1-NIH, which showed the deficiency in the O2 scavenging capacity by the resistant strain to be associated with the hydrogenosome-containing fraction.

Degradative inactivation of the peroxisomal enzyme, alcohol oxidase, during adaptation of methanol-grown Candida boidinii to ethanol

Adaptation of methanol-grown C. boidinii to ethanol-utilization in non-growing cells resulted in decreased activity of the peroxisomal enzyme alcohol oxidase. Re-appearance of alcohol oxidase activity was dependent on protein synthesis de novo. Degradation of alcohol oxidase protein was shown to parallel the decrease in activity. Adaptation of methanol-grown cells to ethanol-utilization resulted in increased absorbance due to cytochromes and decreased absorbance due to flavoprotein. Decrease in alcohol oxidase activity was associated with loss of the flavin coenzyme, FAD, from the organisms and the appearance of flavins (FAD, FMN, riboflavin) in the surrounding medium. Electron microscopic observations showed that general degradation of whole peroxisomes rather than specific loss of crystalline cores (alcohol oxidase protein) occurred during the adaptation.

The methane mono-oxygenase reaction system studied in vivo by membrane-inlet mass spectrometry

A membrane-inlet mass spectrometer connected to an open-system cuvette was used for direct measurement of dissolved methane and O2 in bacterial samples of strain OU-4-1, a type II methanotrophic bacterium. A technique was applied for keeping the concentration of dissolved methane or O2 in the sample constant while the concentration of the other dissolved gas was varied. This allowed the reaction mechanism of methane mono-oxygenase to be studied in vivo. The enzyme was found to follow a random bi-reactant mechanism with respect to binding of methane and O2. Binding of one substrate decreased the affinity for the other. The true binding constants were 1 microM for methane and 0.14 microM for O2. Studies of HCN inhibition confirmed the random bi-reactant mechanism. HCN was found to be a non-exclusive inhibitor with a binding constant of 0.4 microM.

Cytochrome o as a terminal oxidase and receptor for aerotaxis in Salmonella typhimurium

Cytochrome o was the only oxidase of the electron transport system that was present in exponentially growing Salmonella typhimurium ST1. Identification of cytochrome o was made by the (CO-reduced)-minus-(reduced) difference spectra and by the photochemical action spectrum of the relief, by light, of CO-inhibited respiration. Cytochrome o also functioned as the receptor for chemotaxis to oxygen (aerotaxis). The concentration of oxygen that elicits the maximum response for aerotaxis (0.7 microM) was similar to the Km for respiration (0.74 microM), and both aerotaxis and respiration were blocked 5 mM KCN.

Oxygen affinity of the respiratory chain of Acanthamoeba castellanii

Apparent Km values for O2 for the soil amoeba Acanthamoeba castellanii determined polarographically and by bioluminescence gave similar values (0.37 and 0.41 microM respectively). Mitochondria oxidizing succinate or NADH in the presence or absence of ADP gave values in the range 0.21-0.36 microM-O2. Oxidation of respiratory-chain components to 50% of the aerobic steady states in intact cells was observed at the following O2 concentrations: cytochrome aa3, 0.1-0.25 microM; cytochrome c, 0.3-0.6 microM; cytochrome b, 0.35-0.45 microM; flavoprotein, 2 microM. In isolated mitochondria corresponding values for a-, c- and b-type cytochromes were 0.007, 0.035-0.05 and 0.06-0.09 microM-O2. It is concluded that an O2 gradient exists between plasma membrane and mitochondria in A. castellanii.

Glycolysis and respiration in yeasts. The Pasteur effect studied by mass spectrometry

Simultaneous and continuous measurements of changes in CO2 and O2 concentrations in glucose-metabolizing yeast suspensions by mass spectrometry enabled a study of the Pasteur effect (aerobic inhibition of glycolysis) in Saccharomyces uvarum and Schizosaccharomyces pombe. A different control mechanism operates in Candida utilis to give a damped oscillation after the anaerobic-aerobic transition. The apparent Km values for respiration of the three yeasts were in the range 1.3-1.8 microM-O2. The apparent Km values for O2 of the Pasteur effect were 5 and 13 microM for catabolite-repressed and derepressed S. uvarum respectively and 7 microM for Sch. pombe. These results are discussed with respect to currently accepted mechanisms for the control of glycolysis.

Photochemical action spectra of CO-liganded terminal oxidases using a liquid dye laser

A method of obtaining photochemical action spectra for the relief of CO inhibition of respiration is described. Continuous readout from a membrane-covered oxygen electrode of dissolved oxygen in a stirred suspension of microorganisms under CO-oxygen gas mixtures in an open reactor enables measurement of increased respiration on illumination. Advantages presented by the use of a liquid dye laser include high intensity of emission and narrow spectral bandwidth; just two dyes (rhodamine 6G and rhodamine 110) are required to match the alpha-absorption maxima of the CO complexes of all known bacterial and mitochondrial terminal oxidases.

Cytochrome a620 in Tetrahymena pyriformis. Reactions with carbon monoxide and oxygen at subzero temperatures and photochemical action spectra

1. Mitochondria-enriched fractions of the ciliate protozoan Tetrahymena pyriformis ST contained CO-reacting cytochromes b560 and a620. 2. A non-photodissociable oxygen-containing compound of cytochrome a620 was formed in whole cell suspensions at -114 degrees C after photolysis of CO in the presence of 200 microM-O2. 3. Electron transport, indicated by the oxidation of cytochrome a620 and cytochrome c, occurred at temperatures higher than -72 degrees C. 4. Photochemical action spectra for the relief of respiratory inhibition of whole cells by CO obtained by using a liquid dye laser indicate that the only CO-reacting terminal oxidase detectable was cytochrome a620. 5. It is concluded that the alternative electron transport chains in this organism utilize non-cytochrome terminal oxidases.

Respiration of the rumen ciliate Dasytricha ruminantium Schuberg

The endogenous respiration of the rumen ciliate Dasytricha ruminantium maintained under an O2 tension of 2kPa (approximately 0.02 atm) was partially inhibited by KCN (40% inhibition) and NaN3 (58% inhibition). The organisms lack cytochromes, and sensitivity of respiration to KCN, NaN3, chloroquine and quercetin suggest that the operation of flavoprotein-iron-sulphur-mediated electron transport. As in Tritrichomonas foetus, hydrogenosomal respiration can be stimulated by the addition of CoA in the presence of 0.025% Triton X-100; stimulation by ADP was not detected. Stimulation of pyruvate-supported O2 uptake by Pi suggests that acetate is produced via acetyl phosphate.