Reaction sites of rotenone, piericidin A, and amytal in relation to the nonheme iron components of NADH dehydrogenase

The insect microbiome is a vast source of bioactive small molecules

Covering: September 1964 to June 2023Bacteria and fungi living in symbiosis with insects have been studied over the last sixty years and found to be important sources of bioactive natural products. Not only classic producers of secondary metabolites such as Streptomyces and other members of the phylum Actinobacteria but also numerous bacteria from the phyla Proteobacteria and Firmicutes and an impressive array of fungi (usually pathogenic) serve as the source of a structurally diverse number of small molecules with important biological activities including antimicrobial, cytotoxic, antiparasitic and specific enzyme inhibitors. The insect niche is often the exclusive provider of microbes producing unique types of biologically active compounds such as gerumycins, pederin, dinactin, and formicamycins. However, numerous insects still have not been described taxonomically, and in most cases, the study of their microbiota is completely unexplored. In this review, we present a comprehensive survey of 553 natural products produced by microorganisms isolated from insects by collating and classifying all the data according to the type of compound (rather than the insect or microbial source). The analysis of the correlations among the metadata related to insects, microbial partners, and their produced compounds provides valuable insights into the intricate dynamics between insects and their symbionts as well as the impact of their metabolites on these relationships. Herein, we focus on the chemical structure, biosynthesis, and biological activities of the most relevant compounds.

Proton-translocating NADH:ubiquinone oxidoreductase of Paracoccus denitrificans plasma membranes catalyzes FMN-independent reverse electron transfer to hexaammineruthenium (III)

NADH-OH, the specific inhibitor of NADH-binding site of the mammalian complex I, is shown to completely block FMN-dependent reactions of P. denitrificans enzyme in plasma membrane vesicles: NADH oxidation (in a competitive manner with K_i of 1 nM) as well as reduction of pyridine nucleotides, ferricyanide and oxygen in the reverse electron transfer. In contrast to these activities, the reverse electron transfer to hexaammineruthenium (III) catalyzed by plasma membrane vesicles is insensitive to NADH-OH. To explain these results, we hypothesize the existence of a non-FMN redox group of P. denitrificans complex I that is capable of reducing hexaammineruthenium (III), which is corroborated by the complex kinetics of NADH: hexaammineruthenium (III)-reductase activity, catalyzed by this enzyme. A new assay procedure for measuring succinate-driven reverse electron transfer catalyzed by P. denitrificans complex I to hexaammineruthenium (III) is proposed.

AMPK-deficiency forces metformin-challenged cancer cells to switch from carbohydrate metabolism to ketogenesis to support energy metabolism

Epidemiologic studies in diabetic patients as well as research in model organisms have indicated the potential of metformin as a drug candidate for the treatment of various types of cancer, including breast cancer. To date most of the anti-cancer properties of metformin have, in large part, been attributed either to the inhibition of mitochondrial NADH oxidase complex (Complex I in the electron transport chain) or the activation of AMP-activated kinase (AMPK). However, it is becoming increasingly clear that AMPK activation may be critical to alleviate metabolic and energetic stresses associated with tumor progression suggesting that it may, in fact, attenuate the toxicity of metformin instead of promoting it. Here, we demonstrate that AMPK opposes the detrimental effects of mitochondrial complex I inhibition by enhancing glycolysis at the expense of, and in a manner dependent on, pyruvate availability. We also found that metformin forces cells to rewire their metabolic grid in a manner that depends on AMPK, with AMPK-competent cells upregulating glycolysis and AMPK-deficient cell resorting to ketogenesis. In fact, while the killing effects of metformin were largely rescued by pyruvate in AMPKcompetent cells, AMPK-deficient cells required instead acetoacetate, a product of fatty acid catabolism indicating a switch from sugar to fatty acid metabolism as a central resource for ATP production in these cells. In summary, our results indicate that AMPK activation is not responsible for metformin anticancer activity and may instead alleviate energetic stress by activating glycolysis.

LXR-Mediated Regulation of Marine-Derived Piericidins Aggravates High-Cholesterol Diet-Induced Cholesterol Metabolism Disorder in Mice

Reported as two antirenal cell carcinoma (RCC) drug candidates, marine-derived compounds piericidin A (PA) and glucopiericidin A (GPA) exhibit hepatotoxicity in renal carcinoma xenograft mice. Proteomics and transcriptomics reveal the hepatotoxicity related with cholesterol disposition since RCC is characterized by cholesterol accumulation. PA/GPA aggravate hepatotoxicity in high-cholesterol diet (HCD)-fed mice while exhibiting no toxicity in chow diet-fed mice. High cholesterol accumulation in liver is liver X receptor (LXR)-mediated cytochrome P450 family 7 subfamily a member 1 (CYP7A1) depression and low-density lipoprotein receptor (LDLR) activation. The farnesoid X nuclear receptor (FXR) is also depressed with a downregulated target gene OSTα. Different from PA directly combined with LXRα as an inhibitor, GPA exists as a prodrug in the liver and exerts toxic effects due to transformation into PA. Surface plasmon resonance (SPR) and docking results of 17 piericidins illustrate that glycosides exert no LXRα binding activity. A longer survival time of GPA-treated mice indicates that further exploration in anti-RCC drug research should focus on reducing glycosides transformed into PA and concentrating in the kidney tumor rather than the liver for lowering the risk of hepatotoxicity.

Effective Generation of Glucosylpiericidins with Selective Cytotoxicities and Insights into Their Biosynthesis

Exploring unknown glycosyltransferases (GTs) is important for compound structural glycodiversification during the search for drug candidates. Piericidin glycosides have been reported to have potent bioactivities; however, the GT responsible for piericidin glucosylation remains unknown. Herein, BmmGT1, a macrolide GT with broad substrate selectivity and isolated from Bacillus methylotrophicus B-9987, was found to be able to glucosylate piericidin A1 in vitro. Next, the codon-optimized GT gene sbmGT1, which was designed based on BmmGT1, was heterologously expressed in the piericidin producer Streptomyces youssoufiensis OUC6819. Piericidin glycosides thus significantly accumulated, leading to the identification of four new glucopiericidins (compounds 3, 4, 6, and 7). Furthermore, using BmmGT1 as the probe, GT1507 was identified in the genome of S. youssoufiensis OUC6819 and demonstrated to be associated with piericidin glucosylation; the overexpression of this gene led to the identification of another new piericidin glycoside, N-acetylglucosamine-piericidin (compound 8). Compounds 4, 7, and 8 displayed cytotoxic selectivity toward A549, A375, HCT-116, and HT-29 solid cancer cell lines compared to the THP-1 lymphoma cell line. Moreover, database mining of GT1507 homologs revealed their wide distribution in bacteria, mainly in those belonging to the high-GC Gram-positive and Firmicutes clades, thus representing the potential for identification of novel tool enzymes for compound glycodiversification. IMPORTANCE Numerous bioactive natural products are appended with sugar moieties and are often critical for their bioactivities. Glycosyltransferases (GTs) are powerful tools for the glycodiversification of natural products. Although piericidin glycosides display potent bioactivities, the GT involved in glucosylation is unclear. In this study, five new piericidin glycosides (compounds 3, 4, 6, 7, and 8) were generated following the overexpression of GT-coding genes in a piericidin producer. Three of them (compounds 4, 7, and 8) displayed cytotoxic selectivity. Notably, GT1507 was demonstrated to be related to piericidin glucosylation in vivo. Furthermore, mining of GT1507 homologs from the GenBank database revealed their wide distribution across numerous bacteria. Our findings would greatly facilitate the exploration of GTs to glycodiversify small molecules in the search for drug candidates.

Docosahexanoic acid signals through the Nrf2-Nqo1 pathway to maintain redox balance and promote neurite outgrowth

Evidence suggests that n-3 polyunsaturated fatty acids may act as activators of the Nrf2 antioxidant pathway. The antioxidant response, in turn, promotes neuronal differentiation and neurite outgrowth. Nrf2 has recently been suggested to be a cell intrinsic mediator of docosohexanoic acid (DHA) signaling. In the current study, we assessed whether DHA-mediated axodendritic development was dependent on activation of the Nrf2 pathway and whether Nrf2 protected from agrochemical-induced neuritic retraction. Expression profiling of the DHA-enriched Fat-1 mouse brain relative to wild type showed a significant enrichment of genes associated with neuronal development and neuronal projection and genes associated with the Nrf2-transcriptional pathway. Moreover, we found that primary cortical neurons treated with DHA showed a dose-dependent increase in Nrf2 transcriptional activity and Nrf2-target gene expression. DHA-mediated activation of Nrf2 promoted neurite outgrowth and inhibited oxidative stress-induced neuritic retraction evoked by exposure to agrochemicals. Finally, we provide evidence that this effect is largely dependent on induction of the Nrf2-target gene NAD(P)H: (quinone acceptor) oxidoreductase 1 (NQO1), and that silencing of either Nrf2 or Nqo1 blocks the effects of DHA on the axodendritic compartment. Collectively, these data support a role for the Nrf2-NQO1 pathway in DHA-mediated axodendritic development and protection from agrochemical exposure.

Brain Hepcidin Suppresses Major Pathologies in Experimental Parkinsonism

Despite intensive research on Parkinson disease (PD) for decades, this common neurodegenerative disease remains incurable. We hypothesize that abnormal iron accumulation is a common thread underlying the emergence of the hallmarks of PD, namely mitochondrial dysfunction and α-synuclein accumulation. We investigated the powerful action of the main iron regulator hepcidin in the brain. In both the rotenone and 6-hydroxydopamine models of PD, overexpression of hepcidin by means of a virus-based strategy prevented dopamine neuronal loss and suppressed major pathologies of Parkinsonism as well as motor deficits. Hepcidin protected rotenone-induced mitochondrial deficits by reducing cellular and mitochondrial iron accumulation. In addition, hepcidin decreased α-synuclein accumulation and promoted clearance of α-synuclein through decreasing iron content that leads to activation of autophagy. Our results not only pinpoint a critical role of iron-overload in the pathogenesis of PD but also demonstrate that targeting brain iron levels through hepcidin is a promising therapeutic direction.

Development of Glucose Transporter (GLUT) Inhibitors

The discovery of novel compound classes endowed with biological activity is at the heart of chemical biology and medicinal chemistry research. This enables novel biological insights and inspires new approaches to the treatment of diseases. Cancer cells frequently exhibit altered glycolysis and glucose metabolism and an increased glucose demand. Thus, targeting glucose uptake and metabolism may open up novel opportunities for the discovery of compounds that differentiate between normal and malignant cells. This review discusses the different chemical approaches to the development of novel inhibitors of glucose uptake through facilitative glucose transporters (GLUTs), and focusses on the most advanced and potent inhibitor classes known to date. GLUT inhibitors may find application not only in the treatment of cancer, but also of other proliferative diseases that exhibit glucose addiction.

Rotenone-induced inner retinal degeneration via presynaptic activation of voltage-dependent sodium and L-type calcium channels in rats

Rotenone, a mitochondrial complex I inhibitor, causes retinal degeneration via unknown mechanisms. To elucidate the molecular mechanisms of its action, we further characterized a rat model of rotenone-induced retinal degeneration. Intravitreal injection of rotenone (2 nmol/eye) damaged mainly the inner retinal layers, including cell loss in the ganglion cell and inner nuclear layers, which were very similar to those induced by 10 nmol/eye N-methyl-D-aspartate (NMDA). These morphological changes were accompanied by the reduced b-wave amplitude of electroretinogram, and increased immunostaining of 2,4-dinitrophenyl, an oxidative stress marker. Rotenone also downregulated expression of neurofilament light-chain gene (Nfl) as a retinal ganglion cell (RGC) marker. This effect was prevented by simultaneous injection of rotenone with antioxidants or NMDA receptor antagonists. More importantly, voltage-dependent sodium and L-type calcium channel blockers and intracellular calcium signaling modulators remarkably suppressed rotenone-induced Nfl downregulation, whereas none of these agents modified NMDA-induced Nfl downregulation. These results suggest that rotenone-induced inner retinal degeneration stems from indirect postsynaptic NMDA stimulation that is triggered by oxidative stress-mediated presynaptic intracellular calcium signaling via activation of voltage-dependent sodium and L-type calcium channels.

Coenzyme Q2 is a universal substrate for the measurement of respiratory chain enzyme activities in trypanosomatids

The measurement of respiratory chain enzyme activities is an integral part of basic research as well as for specialized examinations in clinical biochemistry. Most of the enzymes use ubiquinone as one of their substrates. For current in vitro measurements, several hydrophilic analogues of native ubiquinone are used depending on the enzyme and the workplace. We tested five readily available commercial analogues and we showed that Coenzyme Q₂ is the most suitable for the measurement of all tested enzyme activities. Use of a single substrate in all laboratories for several respiratory chain enzymes will improve our ability to compare data, in addition to simplifying the stock of chemicals required for this type of research.

Characterization of the positive SARP family regulator PieR for improving piericidin A1 production in Streptomyces piomogeues var. Hangzhouwanensis

Piericidin A1, a member of ɑ-pyridone antibiotic, exhibits various biological activities such as antimicrobial, antifungal, and antitumor properties and possesses potent respiration-inhibitory activity against insects due to its competitive binding capacity to mitochondrial complex I. The biosynthetic pathway of piericidin A1 has been reported in Streptomyces piomogeues var. Hangzhouwanensis, while the regulatory mechanism remains poorly understood. In this study, a Streptomyces antibiotic regulatory protein (SARP) family transcriptional regulator PieR was characterized. Genetic disruption and complementation manipulations revealed that PieR positively regulated the production of piericidin A1. Moreover, the overexpression of pieR contributed to the improvement of piericidin A1 productivity. The real-time quantitative PCR (RT-qPCR) was carried out and the data showed that pieR stimulated the transcription of all the biosynthesis-related genes for piericidin A1. In order to explore the regulatory mechanism, electrophoresis mobility shift assays (EMSA) and DNase I footprinting experiments have been conducted. A protected region covering 50 nucleotides within the upstream region of pieR was identified and two 5-nt direct repeat sequences (5′-CCGGA-3′) in the protected region were found. These findings, taken together, set stage for transcriptional control engineering in the view of optimizing piericidin A1 production and thus provide a viable potent route for the construction of strains with high productivity.

Neurobehavioural Changes in a Hemiparkinsonian Rat Model Induced by Rotenone

INTRODUCTION

Rotenone, a mitochondrial complex I inhibitor is used as a neurotoxin agent to reproduce the neuropathological, and behavioural feature of Parkinson's Disease (PD) in rat. Due to acute and chronic exposure of rotenone with various doses through different routes of administration, mortality is being reported. Low dose takes a longer duration to produce PD symptoms in animals. This present study was designed to create hemiparkinsonian 'partial' lesion model by rotenone at a single moderate dose in two sites of striatum in albino rats and also to assess its toxicity by behavioural parameters and by microscopic study.

AIM

To assess all the motor deficits in lesioned animals that are due to the depletion of dopaminergic neurons or its terminals, the lesioned animals were administered with anti-parkinsonian drug, Levodopa which should counteract motor deficits in rats.

MATERIALS AND METHODS

The unilateral partially lesioned PD model was induced by rotenone stereotaxically into two sites of striatum of male Wistar albino rats at a dosage of 25 μg of rotenone/site. Rats were tested for its neurobehavioural activity on 7^th day, 14^th day, 21^st day and on 30^th day after rotenone infusion and compared with the sham group and sacrificed on 21^st and 30^th day for microscopic studies. L-DOPA was administered from 21^st day to 30^th day after lesion and compared with the lesioned group for the motor performance and sacrificed on 30^th day for histology. Statistical analysis using One-way Analysis of variance followed by Tukey's test was applied for behavioural studies.

RESULTS

Statistical analysis showed that the signs and symptoms like motor in-coordination and postural disturbances are highly significant (p<0.05) on 14^th and 21^st day after administration of rotenone when compared to sham group. In L-DOPA treated rats, all the motor deficits were reversed. The neuronal cell death was minimal and sprouting of nerve terminals was detected. In lesioned group, the degeneration of nerve terminals and striatal neurons were in progressive manner.

CONCLUSION

These findings suggest that intrastriatal infusion of rotenone at a moderate dose could be used for producing hemiparkinsonian partially lesioned animal model without any mortality. Hence, this model is suitable for evaluating behavioural studies and in drug screening programs even for a long term study.

Screening and target identification of bioactive compounds that modulate cell migration and autophagy

Cell migration is a fundamental step for embryonic development, wound repair, immune responses, and tumor cell invasion and metastasis. It is well known that protrusive structures, namely filopodia and lamellipodia, can be observed at the leading edge of migrating cells. The formation of these structures is necessary for cell migration; however, the molecular mechanisms behind the formation of these structures remain largely unclear. Therefore, bioactive compounds that modulate protrusive structures are extremely powerful tools for studying the mechanisms behind the formation of these structures and subsequent cell migration. Therefore, we have screened for bioactive compounds that inhibit the formation of filopodia, lamellipodia, or cell migration from natural products, and attempted to identify the target molecules of our isolated compounds. Additionally, autophagy is a bulk, non-specific protein degradation system that is involved in the pathogenesis of cancer and neurodegenerative disorders. Recent extensive studies have revealed the molecular mechanisms of autophagy, however, they also remain largely unclear. Thus, we also have screened for bioactive compounds that modulate autophagy, and identified the target molecules. In the present article, we introduce the phenotypic screening system and target identification of four bioactive compounds.

Discovery of novel drug targets and their functions using phenotypic screening of natural products

Natural products are valuable resources that provide a variety of bioactive compounds and natural pharmacophores in modern drug discovery. Discovery of biologically active natural products and unraveling their target proteins to understand their mode of action have always been critical hurdles for their development into clinical drugs. For effective discovery and development of bioactive natural products into novel therapeutic drugs, comprehensive screening and identification of target proteins are indispensable. In this review, a systematic approach to understanding the mode of action of natural products isolated using phenotypic screening involving chemical proteomics-based target identification is introduced. This review highlights three natural products recently discovered via phenotypic screening, namely glucopiericidin A, ecumicin, and terpestacin, as representative case studies to revisit the pivotal role of natural products as powerful tools in discovering the novel functions and druggability of targets in biological systems and pathological diseases of interest.

Pioglitazone leads to an inactivation and disassembly of complex I of the mitochondrial respiratory chain

BACKGROUND

Thiazolidinediones are antidiabetic agents that increase insulin sensitivity but reduce glucose oxidation, state 3 respiration, and activity of complex I of the mitochondrial respiratory chain (MRC). The mechanisms of the latter effects are unclear. The aim of this study was to determine the mechanisms by which pioglitazone (PGZ), a member of the thiazolidinedione class of antidiabetic agents, decreases the activity of the MRC. In isolated mitochondria from mouse liver, we measured the effects of PGZ treatment on MRC complex activities, fully-assembled complex I and its subunits, gene expression of complex I and III subunits, and [3H]PGZ binding to mitochondrial complexes.

RESULTS

In vitro, PGZ decreased activity of complexes I and III of the MRC, but in vivo only complex I activity was decreased in mice treated for 12 weeks with 10 mg/kg/day of PGZ. In vitro treatment of isolated liver mitochondria with PGZ disassembled complex I, resulting in the formation of several subcomplexes. In mice treated with PGZ, fully assembled complex I was increased and two additional subcomplexes were found. Formation of supercomplexes CI+CIII2+CIVn and CI+CIII2 decreased in mouse liver mitochondria exposed to PGZ, while formation of these supercomplexes was increased in mice treated with PGZ. Two-dimensional analysis of complex I using blue native/sodium dodecyl sulfate polyacrylamide gel electrophoresis (BN/SDS-PAGE) showed that in vitro PGZ induced the formation of four subcomplexes of 600 (B), 400 (C), 350 (D), and 250 (E) kDa, respectively. Subcomplexes B and C had NADH:dehydrogenase activity, while subcomplexes C and D contained subunits of complex I membrane arm. Autoradiography and coimmunoprecipitation assays showed [3H]PGZ binding to subunits NDUFA9, NDUFB6, and NDUFA6. Treatment with PGZ increased mitochondrial gene transcription in mice liver and HepG2 cells. In these cells, PGZ decreased intracellular ATP content and enhanced gene expression of specific protein 1 and peroxisome-proliferator activated receptor (PPAR)γ coactivator 1α (PGC-1α).

CONCLUSIONS

PGZ binds complex I subunits, which induces disassembly of this complex, reduces its activity, depletes cellular ATP, and, in mice and HepG2 cells, upregulates nuclear DNA-encoded gene expression of complex I and III subunits.

1-Methyl-1,2,3,4-tetrahydroisoquinoline, an endogenous amine with unexpected mechanism of action: new vistas of therapeutic application

This review outlines the effects of 1,2,3,4-tetrahydroisoquinoline (TIQ) and its derivative, 1-methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ), endogenous substances imbued with high pharmacological potential and broad spectrum of action in brain. 1MeTIQ has gained special interest as a neuroprotectant, and its ability to antagonize the behavioral syndrome produced by well-known neurotoxins (e.g., MPTP; rotenone). This review is thus focused on mechanisms of action of 1MeTIQ in behavioral, neurochemical, and molecular studies in rodents; also, effects of TIQ and 1MeTIQ on dopamine metabolism; and neuroprotective properties of TIQ and 1MeTIQ in vitro and in vivo. Finally, antiaddictive properties of 1MeTIQ will be described in cocaine self-administered rats. Findings implicate TIQ and especially its methyl derivative 1MeTIQ in unique and complex mechanisms of neuroprotection in various neurodegenerative illnesses of the central nervous system. We believe that MAO inhibition, free radicals scavenging properties, and antagonism to the glutamatergic system may play an essential role in neuroprotection. In addition, the results strongly support the view that 1MeTIQ has a considerable potential as a drug for combating substance abuse, through the attenuation of craving.

5,6-Dimethylxanthenone-4-acetic acid (DMXAA) activates stimulator of interferon gene (STING)-dependent innate immune pathways and is regulated by mitochondrial membrane potential

The chemotherapeutic agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA) is a potent inducer of type I IFNs and other cytokines. This ability is essential for its chemotherapeutic benefit in a mouse cancer model and suggests that it might also be useful as an antiviral agent. However, the mechanism underlying DMXAA-induced type I IFNs, including the host proteins involved, remains unclear. Recently, it was reported that the antioxidant N-acetylcysteine (NAC) decreased DMXAA-induced TNF-α and IL-6, suggesting that oxidative stress may play a role. The goal of this study was to identify host proteins involved in DMXAA-dependent signaling and determine how antioxidants modulate this response. We found that expression of IFN-β in response to DMXAA in mouse macrophages requires the mitochondrial and endoplasmic reticulum resident protein STING. Addition of the antioxidant diphenylene iodonium (DPI) diminished DMXAA-induced IFN-β, but this decrease was independent of both the NADPH oxidase, Nox2, and de novo generation of reactive oxygen species. Additionally, IFN-β up-regulation by DMXAA was inhibited by agents that target the mitochondrial electron transport chain and, conversely, loss of mitochondrial membrane potential correlated with diminished innate immune signaling in response to DMXAA. Up-regulation of Ifnb1 gene expression mediated by cyclic dinucleotides was also impaired by DPI, whereas up-regulation of Ifnb1 mRNA due to cytosolic double-stranded DNA was not. Although both stimuli signal through STING, cyclic dinucleotides interact directly with STING, suggesting that recognition of DMXAA by STING may also be mediated by direct interaction.

Elucidation of Piericidin A1 biosynthetic locus revealed a thioesterase-dependent mechanism of α-pyridone ring formation

Piericidins are a class of α-pyridone antibiotics that inhibit mitochondrial respiratory chain and exhibit antimicrobial, antifungal, and antitumor activities. Sequential analysis of Streptomyces piomogeues var. Hangzhouwanensis genome revealed six modular polyketide synthases, an amidotransferase, two methyltransferases, and a monooxygenase for piericidin A1 production. Gene functional analysis and deletion results provide overview of the biosynthesis pathway. Furthermore, in vitro characterization of the terminal polyketide synthase module with the thioesterase domain using β-ketoacyl substrates was performed. That revealed a pathway where the α-pyridone ring formation is dependent on hydrolysis of the product β, δ-diketo carboxylic acid by the C-terminal thioesterase followed by amidation and cyclization. These findings set the stage to investigate unusual enzymatic mechanisms in α-pyridone antibiotics biosynthesis, provide a foundation for genome mining of α-pyridone antibiotics, and produce analogs by molecular engineering.

In vitro inhibition of pigmentation and fiber development in colored cotton

Colored cotton has naturally pigmented fibers. The mechanism of pigmentation in cotton fiber is not well documented. This experiment was conducted to study the effects of respiratory chain inhibitors, i.e., rotenone and thiourea, on pigmentation and fiber development in colored cotton. After 1 d post-anthesis, ovaries were harvested and developing ovules were cultured on the liquid medium containing different concentrations of rotenone and thiourea for 30 d. The results demonstrate that both respiratory inhibitors reduced fiber length and ovule development under ovule culture conditions, and the inhibition efficiency of rotenone was much higher than that of thiourea. Rotenone and thiourea also showed significant effects on fiber pigment (color) development in colored cotton. In green cotton fiber, rotenone advanced fiber pigment development by 7 d at 200 μmol/L, while thiourea inhibited fiber pigmentation at all treatment levels (400, 600, 800, 1000, and 2000 μmol/L). Both respiratory inhibitors, however, had no significant effects on pigmentation of brown cotton fibers. The activities of cytochrome c oxidase (COX) and polyphenol oxidase (PPO) decreased significantly with increasing levels of both respiratory inhibitors. It is suggested that both respiratory inhibitors have important roles in deciphering the mechanism of pigmentation and fiber development in colored cotton.

Protection by an antioxidant of rotenone-induced neuromotor decline, reactive oxygen species generation and cellular stress in mouse brain

Exposure to environmental toxins, including rotenone, results in central nervous system and systemic toxicity. Rotenone is a widely used pesticide and a mitochondrial complex I (CI) inhibitor. This study reports effectiveness of a synthetic lipoylcarnitine antioxidant compound, lipoylcarnitine methyl ester iodide (PMX-500F), for treatment of chronic rotenone induced neurological deficits in mice. Mice (C57BL/6NTac; two months of age) received oral administration of rotenone (30 mg/kg/day) or vehicle, preceded by intraperitoneal injection of PMX-500F (19 mg/kg) or vehicle for four weeks. In the Rota-rod test, rotenone treatment had no effect (P>0.05); however, PMX-500F treatment improved locomotor coordination and endurance (latency to fall time; P<0.05). For neuromuscular strength (wire hang test), rotenone treated mice showed reduced latency to fall compared to control mice (P<0.05). PMX-500F treatment improved the outcome in both control and rotenone exposed mice (P<0.05). Rotenone administration increased ROS generation in the forebrain and midbrain regions, but not in the cerebellum (P<0.05). Co-treatment with PMX-500F normalized the ROS in forebrain and midbrain regions to that of the control concentrations. In rotenone administered mice, activated stress-activated protein kinase/c-Jun NH2-terminal kinase (pSAPK/JNK) was higher in forebrain and midbrain lysates than in control mice (P<0.05) and treatment with PMX-500F reduced pSAPK/JNK to control levels. The pSAPK/JNK levels in the cerebellum were similar in all four groups (P>0.05). Total SAPK/JNK was not altered by either rotenone or PMX-500F treatment (P>0.05). These results illustrate that an antioxidant, here PMX-500F, provides protection against rotenone induced decline in neuromotor function, reactive oxygen species (ROS) generation and cellular stress.

Parkinson's disease

Parkinson's disease (PD) is the most common age-related motoric neurodegenerative disease initially described in the 1800's by James Parkinson as the 'Shaking Palsy'. Loss of the neurotransmitter dopamine was recognized as underlying the pathophysiology of the motor dysfunction; subsequently discovery of dopamine replacement therapies brought substantial symptomatic benefit to PD patients. However, these therapies do not fully treat the clinical syndrome nor do they alter the natural history of this disorder motivating clinicians and researchers to further investigate the clinical phenotype, pathophysiology/pathobiology and etiology of this devastating disease. Although the exact cause of sporadic PD remains enigmatic studies of familial and rare toxicant forms of this disorder have laid the foundation for genome wide explorations and environmental studies. The combination of methodical clinical evaluation, systematic pathological studies and detailed genetic analyses have revealed that PD is a multifaceted disorder with a wide-range of clinical symptoms and pathology that include regions outside the dopamine system. One common thread in PD is the presence of intracytoplasmic inclusions that contain the protein, α-synuclein. The presence of toxic aggregated forms of α-synuclein (e.g., amyloid structures) are purported to be a harbinger of subsequent pathology. In fact, PD is both a cerebral amyloid disease and the most common synucleinopathy, that is, diseases that display accumulations of α-synuclein. Here we present our current understanding of PD etiology, pathology, clinical symptoms and therapeutic approaches with an emphasis on misfolded α-synuclein.

Loss of mitochondrial complex I activity potentiates dopamine neuron death induced by microtubule dysfunction in a Parkinson's disease model

The combination of microtubule depolymerization and the accumulation of cytosolic dopamine and reactive oxygen species selectively affects survival of dopaminergic neurons.

Mitochondrial complex I dysfunction is regarded as underlying dopamine neuron death in Parkinson’s disease models. However, inactivation of the Ndufs4 gene, which compromises complex I activity, does not affect the survival of dopamine neurons in culture or in the substantia nigra pars compacta of 5-wk-old mice. Treatment with piericidin A, a complex I inhibitor, does not induce selective dopamine neuron death in either Ndufs4^+/+ or Ndufs4^−/− mesencephalic cultures. In contrast, rotenone, another complex I inhibitor, causes selective toxicity to dopamine neurons, and Ndufs4 inactivation potentiates this toxicity. We identify microtubule depolymerization and the accumulation of cytosolic dopamine and reactive oxygen species as alternative mechanisms underlying rotenone-induced dopamine neuron death. Enhanced rotenone toxicity to dopamine neurons from Ndufs4 knockout mice may involve enhanced dopamine synthesis caused by the accumulation of nicotinamide adenine dinucleotide reduced. Our results suggest that the combination of disrupting microtubule dynamics and inhibiting complex I, either by mutations or exposure to toxicants, may be a risk factor for Parkinson’s disease.

Metabolomic identification of the target of the filopodia protrusion inhibitor glucopiericidin A

Identifying the targets of bioactive compounds is a major challenge in chemical biological research. Here, we identified the functional target of the natural bioactive compound glucopiericidin A (GPA) through metabolomic analysis. We isolated GPA while screening microbial samples for a filopodia protrusion inhibitor. Interestingly, GPA alone did not inhibit filopodia protrusion, but synergistically inhibit protrusion with the mitochondrial respiration inhibitor, piericidin A (PA). These results suggested that GPA might inhibit glycolysis. Capillary electrophoresis time-of-flight mass spectrometry (CE-TOFMS) provided strong evidence that GPA suppresses glycolysis by functionally targeting the glucose transporter. GPA may therefore serve as a glucose transporter chemical probe. Simultaneous inhibition of both glycolysis and mitochondrial respiration dramatically decreased intracellular ATP levels, indicating that GPA inhibits ATP-dependent filopodia protrusion with PA. Our results represent a challenge of molecular target identification using metabolomic analysis.

Both stereoselective (R)- and (S)-1-Methyl-1,2,3,4-tetrahydroisoquinoline enantiomers protect striatal terminals against rotenone-induced suppression of dopamine release

1-Methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ) is present in the human and rodent brain as a mixture of stereospecific (R)- and (S)-1MeTIQ enantiomers. The racemate, (R,S)-1MeTIQ, exhibits neuroprotective activity as shown in the earlier study by the authors, and In addition, it was suggested to play a crucial physiological role in the mammalian brain as an endogenous regulator of dopaminergic activity. In this article, we investigated the influence of stereospecific enantiomers of 1MeTIQ, (R)- and (S)-1MeTIQ (50 mg/kg i.p.) on rotenone-induced (3 mg/kg s.c.) behavioral and neurochemical changes in the rat. In behavioral study, in order to record dynamic motor function of rats, we measured locomotor activity using automated locomotor activity boxes. In biochemical studies, we analyzed in rat striatum the concentration of dopamine (DA) and its metabolites: intraneuronal DOPAC, extraneuronal 3-MT, and final HVA using HPLC with electrochemical detection. Otherwise, DA release was estimated by in vivo microdialysis study. The behavioral study has demonstrated that both acute and repeated (3 times) rotenone administration unimportantly depressed a basic locomotor activity in rat. (R)- and (S)-1MeTIQ stereoisomers (50 mg/kg i.p.) produced a modest behavioral activation both in naïve and rotenone-treated rats. The data from ex vivo neurochemical experiments have shown stereospecificity of 1MeTIQ enantiomers in respect of their effects on DA catabolism. (R)-1MeTIQ significantly increased both the level of the final DA metabolite, HVA (by about 70%), and the rate of DA metabolism (by 50%). In contrast to that, (S)-1MeTIQ significantly depressed DOPAC, HVA levels (by 60 and 40%, respectively), and attenuated the rate of DA metabolism (by about 60%). On the other hand, both the enantiomers increased the concentrations of DA and its extraneuronal metabolite, 3-MT in rat striatum. In vivo microdialysis study has shown that repeated but not acute administration of rotenone produced a deep and significant functional impairment of striatal DA release. Both (R)- and (S)- stereospecific enantiomers of 1MeTIQ antagonized rotenone-induced suppression of DA release; however, the effect of (R)-1MeTIQ was more strongly expressed in microdialysis study. In conclusion, we suggest that both chiral isomers of 1MeTIQ offer neuroprotection against rotenone-induced disturbances in the function of dopaminergic neurons and (R,S)-1MeTIQ will be useful as a drug with marked neuroprotective activity in the brain.

Two different electron transfer pathways may involve in azoreduction in Shewanella decolorationis S12

Electron transfer pathways for azoreduction by S. decolorationis S12 were studied using a mutant S12-22 which had a transposon insertion in ccmA. The results imply that there are two different pathways for electron transport to azo bonds. The colony of S12-22 was whitish and incapable of producing mature c-type cytochromes whose alpha-peak was at 553 nm in the wild type S12. The mutant S12-22 could not use formate as the sole electron donor for azoreduction either in vivo or in vitro, but intact cells of S12-22 were able to reduce azo dyes of low polarity, such as methyl red, when NADH was served as the sole electron donor. Although the highly polar-sulfonated amaranth could not be reduced by intact cells of S12-22, it could be efficiently reduced by cell extracts of the mutant when NADH was provided as the sole electron donor. These results suggest that the mature c-type cytochromes are essential electron mediators for the extracellular azoreduction of intact cells, while the other pathway without the involvement of mature c-type cytochromes, NADH-dependent oxidoreductase-mediated electron transfer pathway can reduce lowly polar sulfonated azo dyes inside the whole cells or highly polar sulfonated azo dyes in the cell extracts without bacterial membrane barriers.

Striatal neuroprotection with methylene blue

Recent literature indicates that low-dose Methylene Blue (MB), an autoxidizable dye with powerful antioxidant and metabolic enhancing properties, might prevent neurotoxin-induced neural damage and associated functional deficits. This study evaluated whether local MB may counteract the anatomical and functional effects of the intrastriatal infusion of the neurotoxin rotenone (Rot) in the rat. To this end, stereological analyses of striatal lesion volumes were performed and changes in oxidative energy metabolism in the striatum and related motor regions were mapped using cytochrome oxidase histochemistry. The influence of MB on striatal levels of oxidative stress induced by Rot was determined, and behavioral tests were used to investigate the effect of unilateral MB coadministration on motor asymmetry. Rot induced large anatomical lesions resembling "metabolic strokes," whose size was greatly reduced in MB-treated rats. Moreover, MB prevented the decrease in cytochrome oxidase activity and the perilesional increase in oxidative stress associated with Rot infusion in the striatum. MB also prevented the indirect effects of the Rot-induced lesion on cytochrome oxidase activity in related motor regions, such as the striatal regions rostral and caudal to the lesion, the substantia nigra compacta and reticulata, and the pedunculopontine nucleus. At a network level, MB maintained a global strengthening of functional connectivity in basal ganglia-thalamocortical motor circuits, as opposed to the functional decoupling observed in Rot-alone subjects. Finally, MB partially prevented the behavioral sensorimotor asymmetries elicited by Rot. These results are consistent with protective effects of MB against neurotoxic damage in the brain parenchyma. This study provides the first demonstration of the anatomical, metabolic and behavioral neuroprotective effects of MB in the striatum in vivo, and supports the notion that MB could be a valuable intervention against neural damage associated with oxidative stress and energy hypometabolism.

The protonmotive force is required for maintaining ATP homeostasis and viability of hypoxic, nonreplicating Mycobacterium tuberculosis

The persistence of Mycobacterium tuberculosis despite prolonged chemotherapy represents a major obstacle for the control of tuberculosis. The mechanisms used by Mtb to persist in a quiescent state are largely unknown. Chemical genetic and genetic approaches were used here to study the physiology of hypoxic nonreplicating mycobacteria. We found that the intracellular concentration of ATP is five to six times lower in hypoxic nonreplicating Mtb cells compared with aerobic replicating bacteria, making them exquisitely sensitive to any further depletion. We show that de novo ATP synthesis is essential for the viability of hypoxic nonreplicating mycobacteria, requiring the cytoplasmic membrane to be fully energized. In addition, the anaerobic electron transport chain was demonstrated to be necessary for the generation of the protonmotive force. Surprisingly, the alternate ndh-2, but not -1, was shown to be the electron donor to the electron transport chain and to be essential to replenish the [NAD(+)] pool in hypoxic nonreplicating Mtb. Finally, we describe here the high bactericidal activity of the F(0)F(1) ATP synthase inhibitor R207910 on hypoxic nonreplicating bacteria, supporting the potential of this drug candidate for shortening the time of tuberculosis therapy.

Characterization of the NADH:ubiquinone oxidoreductase (complex I) in the trypanosomatid Phytomonas serpens (Kinetoplastida)

NADH dehydrogenase activity was characterized in the mitochondrial lysates of Phytomonas serpens, a trypanosomatid flagellate parasitizing plants. Two different high molecular weight NADH dehydrogenases were characterized by native PAGE and detected by direct in-gel activity staining. The association of NADH dehydrogenase activities with two distinct multisubunit complexes was revealed in the second dimension performed under denaturing conditions. One subunit present in both complexes cross-reacted with the antibody against the 39 kDa subunit of bovine complex I. Out of several subunits analyzed by MS, one contained a domain characteristic for the LYR family subunit of the NADH:ubiquinone oxidoreductases. Spectrophotometric measurement of the NADH:ubiquinone 10 and NADH:ferricyanide dehydrogenase activities revealed their different sensitivities to rotenone, piericidin, and diphenyl iodonium.

Systematic administration of iptakalim, an ATP-sensitive potassium channel opener, prevents rotenone-induced motor and neurochemical alterations in rats

Our previous studies revealed that iptakalim, a novel ATP-sensitive potassium channel opener, has a significant neuroprotective function against ischemia in vivo or rotenone-induced neurotoxicity in vitro. To investigate the potential pharmaceutical benefit of ATP-sensitive potassium channel openers on neurodegenerative diseases, we studied the effects of iptakalim and diazoxide, a selective mitochondrial ATP-sensitive potassium channel opener, on the rotenone-induced nigrostriatal degeneration in rats. Iptakalim (1.5 mg/kg/day, orally) or diazoxide (1.5 mg/kg/day, orally) alone was administered to rats for 3 days, and then for 4 weeks was used daily with an injection of rotenone (2.5 mg/kg/day, subcutaneously) 1 hr later each time. The results showed that rotenone-infused rats exhibited parkinsonian symptoms and had dopamine depletion in the striatum and substantia nigra. Pretreatment with iptakalim or diazoxide prevented rotenone-induced catalepsy and the reduction of striatum dopamine contents. Moreover, iptakalim and diazoxide reduced the enzymatic activities and mRNA levels of inducible nitric oxide synthase elicited by chronic administration of rotenone. These neuroprotective effects of iptakalim and diazoxide were abolished by 5-hydroxydecanoate, a selective mitochondrial ATP-sensitive potassium channel blocker. In conclusion, our data suggested that mitochondrial ATP-sensitive potassium channels might play a key role in preventing both parkinsonian symptoms and neurochemistry alterations induced by rotenone in rats. The selective activation of mitochondrial ATP-sensitive potassium channels may provide a new therapeutic strategy for prevention and treatment of neurodegenerative disorders such as Parkinson's disease.

1-methyl-1,2,3,4-tetrahydroisoquinoline protects against rotenone-induced mortality and biochemical changes in rat brain

The effect of single and multiple administration of the neurotoxic pesticide, rotenone, and the potentially neuroprotective compound, 1-methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ), on the concentration of dopamine and its metabolites (homovanillic acid-HVA, 3,4-dihydroxyphenylacetic acid-DOPAC, and 3-methoxytyramine-3-MT)) in three brain areas was studied by high-performance liquid chromatography (HPLC) with electrochemical detection in Wistar rats. The rate of dopamine catabolism in the striatum along the N-oxidative and O-methylation pathways was assessed by calculation of the ratio of dopamine metabolites to dopamine. In addition, the effect of rotenone on mortality and general behavior of rats was investigated. We have found that the neurotoxic pesticide, rotenone, administered in a single dose (12 mg/kg s.c.) did not produce evident behavioral or biochemical effects. In contrast, repeated administration of rotenone in doses (12-15 mg/kg) causing abnormalities in general behavior, produced considerable mortality and dramatic increases in dopamine metabolism, which may be ascribed to an increase in the oxidative pathway. Interestingly, it depressed the concentration of the extracellular dopamine metabolite, 3-MT. These behavioral and biochemical changes were effectively counteracted by administration of 1MeTIQ before each dose of rotenone. In summary, we demonstrated that multiple systemic rotenone injections are strongly toxic, and induce alterations of cerebral dopamine metabolism, and that 1MeTIQ may be considered as a potential protective agent against environmental factors affecting the function of the dopaminergic system.

Preliminary assays indicate that Antonia ovata (Loganiaceae) and Derris amazonica (Papilionaceae), ichthyotoxic plants used for fishing in Roraima, Brazil, have an insecticide effect on Lutzomyia longipalpis (Diptera: Psychodidae: Phlebotominae)

Laboratory-reared Lutzomyia longipalpis (Lutz and Neiva 1912) was tested with extracts of two ichthyotoxic plants, known as timbós, used as fishing poison in the Amazon. Phlebotomines, L. longipalpis, and plants, Antonia ovata and Derris amazonica, were collected in the Raposa-Serra do Sol Indian Reserve, a focus of visceral leishmaniasis in the State of Roraima, Brazil. Extracts were prepared from dried leaves of A. ovata and roots of D. amazonica that were percolated in water, filtered and dried out at 50 degrees C. The solid extract obtained was diluted in water at 150, 200 and 250 mg/ml. The solution was blotted in filter paper placed at the bottom of cylindric glass tubes containing sand flies. For each plant extract and dilution, two series of triplicates with 5 male and 5 female specimens of L. longipalpis were used. Mortality was recorded every 2 h during 72 h of exposure. At 72 h the mortality was as high as 80% for extracts of A. ovata (LD50 = 233 mg/ ml), and 100% for D. amazonica (LD50 = 212 mg/ ml) whereas in the control groups maximum mortality never surpassed 13%. Preliminary assays indicated that A. ovata and D. amazonica displayed significant insecticide effect against L. longipalpis.

Amobarbital inhibits K(+)-stimulated glucose oxidation in cerebellar granule neurons by two mechanisms

The study aimed at determining mechanism(s) by which amobarbital (amytal) suppresses glucose oxidation in cerebellar granule neurons in primary cultures, a glutamatergic preparation. When challenged with a depolarizing K(+) concentration (55 mM), the cells doubled their rate of glucose oxidation (production of 14CO(2) from U-[14C]glucose) and glycolysis (lactate accumulation). At normal K(+) concentration, amobarbital reduced 14CO(2) production with half-maximum effect at 0.5-1 mM; at 55 mM K(+), the inhibition was more potent, with more than half of the K(+)-induced stimulation abolished at 50 microM. Dixon plot analysis showed a single inhibitory mechanism at 5.4 mM K(+), but at 55 mM K(+), two kinetically different mechanisms could be distinguished. A more pronounced compensatory amobarbital-induced increase in glycolysis at 5.4 than at 55 mM K(+) suggested that amobarbital in addition to its inhibition of mitochondrial respiration inhibited K(+)-induced increase in energy demand, probably by its known suppression of stimulated glutamate release.

Comparison of the inhibitory action of natural rotenone and its stereoisomers with various NADH-ubiquinone reductases

Two stereoisomers of natural rotenone (5'alpha-epirotenone and 5'beta-epirotenone) were synthesized to identify the stereochemical factor of rotenone required for the inhibition and also to probe the structure of the rotenone binding site. The inhibitory action of the stereoisomers was compared with that of rotenone using NADH-ubiquinone reductases from bovine heart submitochondrial particles (SMP), potato tubers (Solanum tuberosum L.) SMP and Escherichia coli (GR19N) membranes. With respect to bovine heart SMP, it was found that the bent form of rotenone is essential for the activity. The modification of the E-ring moiety also affected both the inhibitory potency and the pattern of inhibition. These results indicated that the rotenone-binding site recognizes the whole molecular structure (or shape) of rotenone in a strict sense. Rotenone and 5'beta-epirotenone inhibited the NADH-ubiquinone reductase of bovine heart SMP in a noncompetitive manner against exogenous quinones. In contrast, the inhibition pattern of 5'alpha-epirotenone varied from noncompetitive to competitive as the concentration of quinone increased. These results suggest that rotenone binds close to, but not at a site identical to, the location for ubiquinone in the ubiquinone-catalytic reaction site, whereas the 5'alpha-epirotenone-binding site overlaps that for ubiquinone due to a structural modification of E-ring moiety. Furthermore, the complex inhibition pattern of 5'alpha-epirotenone suggests that there are two quinone-binding sites in NADH-ubiquinone reductase. In contrast, the order of the inhibitory potencies of the three inhibitors with proton-pumping NADH-ubiquinone reductase of potato SMP was the same as that observed for the bovine enzyme. This suggests that the structure of rotenone-binding sites (or ubiquinone-binding sites) of these enzymes are similar. It was further demonstrated that 5'alpha-epirotenone inhibits quinone binding to both proton-pumping and non-proton-pumping NADH-ubiquinone reductases of potato SMP in a competitive manner. With respect to the proton-pumping NADH-ubiquinone reductase of the E. coli membrane, the sensitivity of the enzyme to the inhibitor was remarkably decreased and the difference in the inhibitory potencies of the three inhibitors became ambiguous. In addition, the inhibition pattern of the three inhibitors was competitive against quinone. These results indicated that, contrary to the mammalian enzyme, only part of the rotenone molecule is recognized by the quinone-binding site of this enzyme.

Interaction of 1-methyl-4-phenylpyridinium ion (MPP+) and its analogs with the rotenone/piericidin binding site of NADH dehydrogenase

Nigrostriatal cell death in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced Parkinson's disease results from the inhibition of mitochondrial respiration by 1-methyl-4-phenylpyridinium (MPP+). MPP+ blocks electron flow from NADH dehydrogenase to coenzyme Q at or near the same site as do rotenone and piericidin and protects against binding of and loss of activity due to these inhibitors. The 4'-analogs of MPP+ showed increasing affinity for the site with increasing length of alkyl chain, with the lowest Ki, for 4'-heptyl-MPP+, being 6 microM. The 4'-analogs compete with rotenone for the binding site in a concentration-dependent manner. They protect the activity of the enzyme from inhibition by piericidin in parallel to preventing its binding, indicating that the analogs and piericidin bind at the same inhibitory site(s). The optimum protection, however, was afforded by 4'-propyl-MPP+. The lesser protection by the more lipophilic MPP+ analogs with longer alkyl chains may involve a different orientation in the hydrophobic cleft, allowing rotenone and piericidin to still bind even when the pyridinium cation is in a position to interrupt electron flow from NADH to coenzyme Q.

Evidence that the inhibition sites of the neurotoxic amine 1-methyl-4-phenylpyridinium (MPP+) and of the respiratory chain inhibitor piericidin A are the same

1-Methyl-4-phenylpyridinium (MPP+), the neurotoxic bioactivation product of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), interrupts mitochondrial electron transfer at the NADH dehydrogenase-ubiquinone junction, as do the respiratory chain inhibitors rotenone, piericidin A and barbiturates. Proof that these classical respiratory chain inhibitors and MPP+ react at the same site in the complex NADH dehydrogenase molecule has been difficult to obtain because none of these compounds bind covalently to the target. The 4'-alkyl derivatives of MPP+ inhibit NADH oxidation in submitochondrial particles at much lower concentrations than does MPP+ itself, but still dissociate on washing the membrane preparations, with consequent re-activation of the enzyme. The MPP+ analogues with short alkyl chains prevent the binding of 14C-labelled piericidin A to the membrane and thus must act at the same site, but analogues with alkyl chains longer than heptyl do not prevent binding of [14C]piericidin.

Respiration of Gametangia of the Aquatic Phycomycete Allomyces macrogynus: Inhibition by Cyanide or Antimycin and Salicylhydroxamic Acid or Propyl Gallate

Gametangia of the aquatic phycomycete Allomyces macrogynus have a cyanide- and antimycin A-insensitive respiration, which is sensitive to salicylhydroxamic acid (alternative respiration). Propyl gallate is also an inhibitor of this alternative pathway, and propyl gallate is more efficient than hydroxamic acid. Gametangial respiration is insensitive to propyl gallate, but propyl gallate sensitivity is gradually established when the gametangia are titrated with cyanide. Carbonyl cyanide m-chlorophenyl hydrazone stimulates the cyanide-sensitive respiration and engages the alternative sensitive respiration. Sodium azide inhibits both the alternative and the cyanide-sensitive respiration, but the cyanide-sensitive respiration is inhibited 10 times more efficiently than the alternative respiration. Rotenone inhibits the total respiration and the propyl gallate-insensitive respiration by 33% and the cyanide-insensitive respiration by 43%.The kinetic results reported here are discussed with respect to the models of de Troostembergh and Nyns (1977 Arch Int Physiol Biochem 85:404-406; 1978 Eur J Biochem 53:423-432) and of Bahr and Bonner (1973 J Biol Chem 248:3446-3450) for the partitioning of electrons between cyanide-insensitive and propyl gallate-insensitive respiration. The results reported here do not agree with the model of de Troostembergh and Nyns.