Properties of mitochondria isolated from cyanide-sensitive and cyanide-stimulated cultures of Acanthamoeba castellanii

1. Mitochondria isolated from cultures of Acanthamoeba castellanii exhibit respiratory control and oxidize alpha-oxoglutarate, succinate and NADH with ADP:O ratios of about 2.4, 1.4 and 1.25 respectively. 2. Mitochondria from cultures of which the respiration was stimulated up to 50% by 1mm-cyanide (type-A mitochondria) and from cyanide-sensitive cultures (type-B mitochondria) had similar respiratory-control ratios and ADP:O ratios. 3. State-3 rates of respiration were generally more cyanide-sensitive than State-4 rates, and the respiration of type-A mitochondria was more cyanide-resistant than that of type-B mitochondria. 4. Salicylhydroxamic acid alone had little effect on respiratory activities of either type of mitochondria, but when added together with cyanide, irrespective of the order of addition, inhibition was almost complete. 5. Oxidation of externally added NADH by type-A mitochondria was mainly via an oxidase with a low affinity for oxygen (K(m)[unk]15mum), which was largely cyanide-sensitive and partially antimycin A-sensitive; this electron-transport pathway was inhibited by ADP. 6. Cyanide-insensitive but salicylhydroxamic acid-sensitive respiration was stimulated by AMP and ADP, and by ATP after incubation in the presence of MgCl(2). 7. Addition of rotenone to mitochondria oxidizing alpha-oxoglutarate lowered the ADP:O ratios by about one-third and rendered inhibition by cyanide more complete. 8. The results suggest that mitochondria of A. castellanii possess branched pathways of electron transport which terminate in three separate oxidases; the proportions of electron fluxes via these pathways vary at different stages of growth.     

Stimulation by quinones of cyanide-resistant respiration in rat liver and heart mitochondria

It was shown that hydrophilic benzo- and naphthoquinones stimulate the cyanide-resistant respiration in liver and muscle mitochondria when succinate or NADH and glutamate or malate are used as oxidation substrates. The substrate-dependent oxygen uptake in the presence of cyanide is initiated by menadione, vicasol, 1.2-naphthoquinone, coenzyme Q0 and duroquinone. Rotenone and antimycin A do not inhibit the cyanide-resistant respiration. Oxidation of glutamate and malate in the course of CN-resistant respiration is inhibited by ortho- and bathophenanthroline and p-chloromercurybenzoate, whereas succinate oxidation by tenoyltrifluoroacetone, carboxin and pentachlorophenol. Superoxide dismutase, Cu2+ and catalase inhibit the CN-resistant respiration in the presence of quinones. Addition of catalase to the experimental cell causes O2 release.     

Electron Transport and Oxidative Phosphorylation in Arum Spadix Mitochondria

Arum spadix mitochondria exhibited a rapid cyanide-resistantoxygen uptake when oxidizing malate, NADH₂ or succinate, anda slower, cyanide-sensitive oxygen uptake when oxidizing ascorbate+tetramethylphenylenediamine(TMPD). Cytochrome oxidase does not therefore appear to functionas the terminal oxidase in the presence of cyanide, and therather low cytochrome c oxidase activity obtained using ascorbate+TMPDmay exclude it from possessing a major role even in the absenceof cyanide. ATP synthesis has been shown to accompany substrateoxidation. In the presence of antimycin A the P: O ratio accompanyingmalate oxidation was reduced by half, while phosphorylationaccompanying NADH₂ or succinate oxidation was almost completelyabolished. It is proposed that electrons from exogenous NADH₂enter the electron transport chain at a site after that whereendogenous NADH2 donates electrons and that electrons from exogenousNADH₂ are not coupled to ATP synthesis at site 1. The cyanide-resistant,non-phosphorylating electron-transport pathway may functionin the absence of cyanide and account for the low efficiencyof energy conservation observed in this tissue.     

NADPH Oxidase System as a Superoxide-generating Cyanide-Resistant Pathway in the Respiratory Chain of Corynebacterium glutamicum

The respiratory chain of Corynebacterium glutamicum was investigated, especially with respect to a cyanide-resistant respiratory chain bypass oxidase. The membranes of C. glutamicum had NADH, succinate, lactate, and NADPH oxidase activities, and menaquinone, and cytochromes a ₅₉₈, b _562(558), and c ₅₅₀ as respiratory components. The NADH, succinate, lactate, and NADPH oxidase systems, all of which were more cyanide-resistant than N,N,N′,N′-tetramethyl-p-phenylene diamine oxidase activity (cytochrome aa ₃ terminal oxidase), had different sensitivities to cyanide; the cyanide sensitivity of these oxidase systems increased in the order, NADPH, lactate, NADH, and succinate. Taken together with the analysis of redox kinetics in the cytochromes and the effects of respiratory inhibitors, the results suggested that there is a cyanide-resistant bypass oxidase branching at the menaquinone site, besides cyanide-sensitive cytochrome oxidase in the respiratory chain. H⁺/O measurements with resting cells suggested that the cyanide-sensitive respiratory chain has two or three coupling sites, of which one is in NADH dehydrogenase and the others between menaquinone and cytochrome oxidase, but the cyanide-resistant bypass oxidase may not have any proton coupling site. NADPH and lactate oxidase systems were more resistant to UV irradiation than other systems and the UV insensitivity was highest in the NADPH oxidase system, suggesting that a specific quinone resistant to UV or no such a quinone works in at least NADPH oxidase system while the UV-sensitive menaquinone pool does in other oxidase systems. Furthermore, superoxide was generated in well-washed membranes, most strongly in the NADPH oxidase system. Thus, it was suggested that the cyanide-resistant bypass oxidase system of C. glutamicum is related to the NADPH oxidase system, which may be involved in generation of superoxide anions and probably functions together with superoxide dismutase and catalase.     

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.     

Mechanism of Superoxide Anion Generation in Intact Mitochondria in the Presence of Lucigenin and Cyanide

In the presence of cyanide and various respiratory substrates (succinate or pyruvate + malate) addition of high concentrations of lucigenin (400 microM; Luc2+) to rat liver mitochondria can induce a short-term flash of high amplitude lucigenin-dependent chemiluminescence (LDCL). Under conditions of cytochrome oxidase inhibition by cyanide the lucigenin-induced cyanide-resistant respiration (with succinate as substrate) was not inhibited by uncouplers (FCCP) and oligomycin. Increase in transmembrane potential (Deltaphi) value by stimulating F0F1-ATPase functioning (induced by addition of MgATP to the incubation medium) caused potent stimulation of the rate of cyanide-resistant respiration. At high Deltaphi values (in the presence of MgATP) cyanide resistant respiration of mitochondria in the presence of succinate or malate with pyruvate was insensitive to tenoyltrifluoroacetone (TTFA) or rotenone, respectively. However, in both cases respiration was effectively inhibited by myxothiazol or antimycin A. Mechanisms responsible for induction of LDCL and cyanide resistant mitochondrial respiration differ. In contrast to cyanide-resistant respiration, generation of LDCL signal, that was suppressed only by combined addition of Complex III inhibitors, antimycin A and myxothiazol, is a strictly potential-dependent process. It is observed only under conditions of high Deltaphi value generated by F0F1-ATPase functioning. The data suggest lucigenin-induced intensive generation of superoxide anion in mitochondria. Based on results of inhibitor analysis of cyanide-resistant respiration and LDCL, a two-stage mechanism of autooxidizable lucigenin cation-radical (Luc*+) formation in the respiratory chain is proposed. The first stage involves two-electron Luc2+ reduction by Complexes I and II. The second stage includes one-electron oxidation of reduced lucigenin (Luc(2e)). Reactions of Luc(2e) oxidation involve coenzyme Q-binding sites of Complex III. This results in formation of autooxidizable Luc*+ and superoxide anion generation. A new scheme for lucigenin-dependent electron pathways is proposed. It includes formation of fully reduced form of lucigenin and two-electron-transferring shunts of the respiratory chain. Lucigenin-induced activation of superoxide anion formation in mitochondria is accompanied by increase in ion permeability of the inner mitochondrial membrane.     

Direct Inhibition of Plant Mitochondrial Respiration by Elevated CO2

Doubling the concentration of atmospheric CO2 often inhibits plant respiration, but the mechanistic basis of this effect is unknown. We investigated the direct effects of increasing the concentration of CO2 by 360 [mu]L L-1 above ambient on O2 uptake in isolated mitochondria from soybean (Glycine max L. cv Ransom) cotyledons. Increasing the CO2 concentration inhibited the oxidation of succinate, external NADH, and succinate and external NADH combined. The inhibition was greater when mitochondria were preincubated for 10 min in the presence of the elevated CO2 concentration prior to the measurement of O2 uptake. Elevated CO2 concentration inhibited the salicylhydroxamic acid-resistant cytochrome pathway, but had no direct effect on the cyanide-resistant alternative pathway. We also investigated the direct effects of elevated CO2 concentration on the activities of cytochrome c oxidase and succinate dehydrogenase (SDH) and found that the activity of both enzymes was inhibited. The kinetics of inhibition of cytochrome c oxidase were time-dependent. The level of SDH inhibition depended on the concentration of succinate in the reaction mixture. Direct inhibition of respiration by elevated CO2 in plants and intact tissues may be due at least in part to the inhibition of cytochrome c oxidase and SDH.     

Studies on the mechanism of NADPH oxidation by the granule fraction isolated from human resting polymorphonuclear blood cells.

Various factor affecting NADPH-oxidation by resting human leucocyte granules (LG) at acid pH, have been investigated. It was found that: 1) oxidation of NADPH by LG was increasingly inhibited by increased cyanide concentrations in the medium and was abolished by 4 mM cyanide. 2) with or without cyanide in the incubation medium, LG omitted, Mn++ in the presence of NADPH induced superoxide anion (O- WITH 2) production, as evidenced by oxygen consumption and H2O2 production, which were abolished (in the absence of cyanide) by cytochrome C (a potent O- with 2 scavenger). 3) Both NADPH oxidation in the presence of 2 mM cyanide (cyanide-resistant) and in its absence (cyanide-sensitive) by LG occurred only in the presence of Mn++, and both were inhibited by superoxide dismutase. 4) Cyanide-resistant NADPH oxidation by LG generated H2O2, was inhibited by H2O2 and was not modified by "active" catalase. The ratio of cyanide-resistant NADPH oxidation/O2 uptake was 1 up to 1.25 mM NADPH, and increased above this concentration. 5) Cyanide-sensitive NADPH oxidation was inhibited by catalase and increased upon addition of H2O2. The ratio of cyanide-sensitive NADPH oxidation/O2 uptake was 2. It was concluded that after initiation by O - with 2, produced independently of LG, two sequential types of LG dependent NADPH oxidations occur. First, an O - with 2-dependent protein mediated NADPH oxidation (cyanide-resistant) which generates H2O2 and O - with 2 occurs. Second, NADPH peroxidation (cyanide-sensitive) which utilizes H2O2 takes place.     

Pyruvate metabolism in castor-bean mitochondria.

We report the isolation of mitochondria from the endosperm of castor beans (Ricinus communis). These mitochondria oxidized succinate, external NADH, malate and pyruvate with respiratory-control and ADP/O ratios consistent with those found previously with mitochondria from other plant sources. The mitochondria exhibited considerable sensitivity to the electron-transport-chain inhibitors antimycin A and cyanide when oxidizing succinate and external NADH. Pyruvate-dependent O2 uptake was relatively insensitive to these inhibitors, although the residual O2 uptake could be inhibited by salicylhydroxamic acid. We conclude that a cyanide-insensitive alternative terminal oxidase is functional in these mitochondria. However, electrons from the succinate dehydrogenase or external NADH dehydrogenase seem to have no access to this pathway. There is little interconnection between the salicylhydroxamic acid-sensitive and cyanide-sensitive pathways of electron transport. alpha-Cyanocinnamate and its analogues, compound UK5099 [alpha-cyano-beta-(1-phenylindol-3-yl)acrylate] and alpha-cyano-4-hydroxycinnamate, were all found to be potent non-competitive inhibitors of pyruvate oxidation in castor-bean mitochondria. The accumulation of pyruvate by castor-bean mitochondria was determined by using a silicone-oil-centrifugation technique. The accumulation was shown to observe Michaelis-Menten kinetics, with a Km for pyruvate of 0.10 mM and a Vmax. of 0.95 nmol/min per mg of mitochondrial protein. However, the observed rates of pyruvate accumulation were insufficient to account for the pyruvate oxidation rates found in the oxygen-electrode studies. We were able to demonstrate that this is due to the immediate export of the accumulated radiolabel in the form of malate and citrate. Compound UK5099 inhibited the accumulation of [2-14C]pyruvate by castor-bean mitochondria at concentrations similar to those required to inhibit pyruvate oxidation.     

Discrimination between duroquinol oxidase activity and the terminal oxidation step of the cyanide-resistant electron transport pathway of plant mitochondria

Comparison of the cyanide-resistant duroquinol oxidase activity of sub-mitochondrial particles from Arum maculatum L. with their ability to carry out a cyanide-resistant oxidation of NADH and succinate shows that heat-inactivation of the duroquinol oxidase activity does not proportionally affect NADH and succinate oxidation. Moreover, 1 microM antimycin inhibits duroquinol oxidase activity by 50% while not decreasing the rates of NADH and succinate oxidation. Therefore, the cyanide-resistant electron transport does not appear to be mediated by a "duroquinol oxidase", and a convincing proof of the existence of a specific protein acting as a cyanide-resistant oxidase in plant mitochondria is still lacking.     

Characterization of cyanide-resistant respiration and appearance of a 36 kDa protein in mitochondria isolated from antimycin A-treated Hansenula anomala

Mitochondria exhibiting cyanide-resistant respiration were isolated from Hansenula anomala which had been incubated in the presence of antimycin A to induce cyanide-resistant respiration. The cyanide-resistant respiration in isolated mitochondria was not inhibited by antimycin A or myxothiazol, suggesting that the branching of the pathway from the normal cyanide-sensitive pathway takes place at the coenzyme Q level. Analysis of mitochondrial proteins by sodium dodecyl sulfate gel electrophoresis indicated that a 36 kDa protein was induced by antimycin A treatment of the yeast. It is suggested that this protein is a component of the cyanide-resistant respiratory pathway.     

Cyanide-resistant respiration in Streptomyces citreofluorescens

The capacity of Streptomycetes to carry out cyanide-resistant respiration was investigated. With the model strain, Streptomyces citreofluorescens, it was shown that deprivation of glucose followed by transition from exponential to stationary growth was coupled with declining sensitivity of cellular respiration to cyanide ions. Cyanide-resistant oxidase is located within the cytoplasmic membrane. The occurrence of the cyanide-resistant oxidase did not correspond to qualitative changes of cytochrome spectrum. Cytochrome d is involved neither in cyanide-sensitive nor in cyanide-resistant respiratory chain.     

Cyanide-Resistant Respiration in Neurospora crassa

Cell respiration in wild type and poky was studied as part of a long-term investigation of cyanide-resistant respiration in Neurospora. Respiration in wild type proceeds via a cytochrome chain which is similar to that of higher organisms; it is sensitive to antimycin A or cyanide. Poky, on the other hand, respires by means of two alternative oxidase systems. One of these is analogous to the wild-type cytochrome chain in that it can be inhibited by antimycin A or cyanide; this system accounts for as much as 15% of the respiration of poky f(-) and 34% of the respiration of poky f(+). The second oxidase system is unaffected by antimycin A or cyanide at concentrations which inhibit the cytochrome chain maximally. It can, however, be specifically inhibited by salicyl hydroxamic acid. The cyanide-resistant oxidase is not exclusive to poky, but is also present in small quantities in wild type grown under ordinary circumstances. These quantities may be greatly increased (as much as 20-fold) by growing wild type in the presence of antimycin A, cyanide, or chloramphenicol.     

Expression of cytochrome o in hydrogen uptake constitutive mutants of Rhizobium japonicum.

Mutant strains of Rhizobium japonicum constitutive for H2 uptake activity (Hupc) contained significantly more membrane-bound b-type cytochrome than did the wild type when grown heterotrophically. The Hupc strains contained approximately three times more dithionite- and NADH-reducible CO-reactive b-type cytochrome than did the wild type; the absorption features of the CO spectra were characteristic of cytochrome o. This component, designated cytochrome b', was not reduced by NADH in the presence of cyanide. Cytochrome o from the wild type (SR) and cytochrome b' from mutants SR476 and SR481 bound to CO with similar dissociation constants of 5.4, 7.4, and 5.6 microM, respectively. NADH-dependent reduction of cytochrome b' from SR476 and SR481 and the cytochrome o from SR followed pseudo-first-order kinetics with similar rate constants. Based on these spectral, ligand-binding, and kinetic measurements, it was concluded that cytochrome b' expressed by the Hupc mutants is equivalent to cytochrome o found in the wild type. H2, NADH, and succinate each reduced the same amount of total b-type cytochrome in membranes from SR481, and the rate of H2-dependent cytochrome o reduction was significantly less than with succinate or NADH as the reductants. It was concluded that neither cytochrome o nor any b-type cytochrome expressed by the Hupc mutants was unique to the H2 oxidation system. At low O2 concentrations, the inhibition of H2 and NADH oxidase activities by CO closely paralleled the binding of CO to cytochrome o rather than cytochromes a3 or c'. This suggested that NADH and H2 oxidation involved primarily cytochrome o as the terminal oxidase at low O2 tensions.     

Characterization of cyanide-insensitive respiration in mitochondria and submitochondrial particles of Moniliella tomentosa

Mitochondria and submitochondrial particles of the osmophilic yeast-like fungus Moniliella tomentosa may respire by means of two pathways: a normal cytochrome pathway, sensitive to cyanide and antimycin A, and an alternative pathway, which is insensitive to these inhibitors but is specifically inhibited by salicylhydroxamic acid. The affinities of both oxidases for succinate and NADH as substrates, for O(2) as terminal electron acceptor, and for AMP as stimulator of the alternative oxidase were determined. 1. Submitochondrial particles of M. tomentosa may also respire by means of a cyanide-sensitive and/or cyanide-insensitive system. 2. The activities of both oxidases as compared with the total activity are roughly the same in submitochondrial particles as in the original mitochondria. 3. The terminal oxidase of the cyanide-insensitive pathway requires a 10-fold higher O(2) concentration for saturation than does cytochrome c oxidase. 4. The apparent K(m) for succinate is about 3 times higher for the alternative than for the normal oxidase when measured in mitochondria, and 4-10 times higher when measured in submitochondrial particles. The apparent K(m) for NADH is roughly the same for both oxidases. 5. The apparent K(m) values of both oxidases for succinate are always lower in submitochondrial particles than in mitochondria. 6. The apparent K(m) for AMP, acting as a stimulator of the alternative oxidase, is the same (25mum) in mitochondria as in sub-mitochondrial particles. These results are discussed in the light of the structure and localization of the components of the alternative oxidase.     

O2-Polarographic Studies on Soluble and Mitochondrial Enzymes of Crithidia fasciculata; Glycerophosphate Enzymes*

SYNOPSIS. Mitochondrial and supernatant fractions were isolated from Crithidia fasciculata by grinding with neutral alumina and differential centrifugation. Supernatant fractions contained at least 2 NAD-linked enzymes: an α-glycerophosphate dehydrogenase and a malate dehydrogenase. The properties of these enzymes were investigated polarographically with phenazine ethosulfate acting as electron acceptor. Agaricic acid, cinnamic acid and p-NO₂-cinnamic acid were specific inhibitors of the α-glycerophosphate dehydrogenase. Succinate, malate, DL-α-glycerophosphate and NADH stimulated respiration of mitochondrial preparations; O₂ uptake was greatest with succinate. KCN and antimycin A inhibited succinate respiration more than α-glycerophosphate respiration. Amytal did not affect succinate, α-glycerophosphate or NADH oxidation. The trypanocide suramin inhibited mitochondrial respiration at least 77% with each substrate. The relevance of these results to other members of the Trypanosomatidae is discussed.     

Changes in Mitochondrial Respiratory Chain Components of Petunia Cells during Culture in the Presence of Antimycin A

When petunia (Petunia hybrida Vilm, cv Rosy Morn) cells are cultured in the presence of 2 [mu]M antimycin A (AA), respiration proceeds mainly via the cyanide-resistant pathway. Cyanide-resistant respiratory rates were higher in mitochondria from AA cells than in control mitochondria. Compared with control cells, an increase in alternative oxidase protein was observed in AA cells, as well as an increase in ubiquinone (UQ) content. A change in the kinetics of succinate dehydrogenase was observed: there was a much higher activity at high UQ reduction in mitochondria from AA cells compared with control mitochondria. No changes were found for external NADH dehydrogenase kinetics. In AA cells in vivo, UQ reduction was only slightly higher than in control cells, indicating that increased electron transport via the alternative pathway can prevent high UQ reduction levels. Moreover, O2 consumption continues at a similar rate as in control cells, preventing O2 danger. These adaptations to stress conditions, in which the cytochrome pathway is restricted, apparently require, in addition to an increase in alternative oxidase protein, a new setup of the relative amounts and/or kinetic parameters of all of the separate components of the respiratory network.     

O(2) affinity of cross-linked hemoglobins modifies O(2) metabolism in proximal tubules.

Previous experiments using cross-linked tetrameric hemoglobins (XLHb) to perfuse isolated rat kidneys showed that high-O2-affinity XLHb improved proximal tubule function more effectively than low-O2-affinity XLHb. To determine how function was improved, proximal tubule fragments were incubated with albumin, Hb34 [half-saturation point (P50) 34 Torr], or Hb13 (P50 13 Torr) with Po2 values ranging from 22 to 147 Torr. ATP content reflected O2 delivery to mitochondria. Both XLHb increased ATP, Hb34 with Po2 >or= 47 Torr and Hb13 with Po2 相似文献   

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.     

Alternative respiration of fungus <Emphasis Type="Italic">Phycomyces blakesleeanus</Emphasis>

Respiratory characteristics of germinating spores, developing mycelium and mitochondria of the fungus Phycomyces blakesleeanus were investigated by means of oxygen Clark-type electrode. The effects of respiratory inhibitors and metabolic compounds on oxygen consumption were tested. It was demonstrated that P. blakesleeanus apart of cyanide-sensitive respiration, CSR, possess alternative respiration, (cyanide-resistant respiration, CRR) which is constitutive and whose capacity decreases during development. Maximum is observed for activated spores where CRR capacity is significantly greater than CSR. After treatment with antimycin A, a third type of respiration insensitive to antimycin A and low concentration of SHAM (sufficient for inhibition of CRR), but sensitive to cyanide and high concentration of SHAM, has been expressed.