Composition, structure, and function of complex III of the respiratory chain

Molecular strategies of the pygmy grasshopper Eucriotettix oculatus adapting to long-term heavy metal pollution

To study the heavy metal accumulation and its impact on insect exterior and chromosome morphology, and reveal the molecular mechanism of insects adapting to long-term heavy metal compound pollution habitats, this study, in the Diaojiang river basin, which has been polluted by heavy metals(HMs) for nearly a thousand years, two Eucriotettix oculatus populations was collected from mining and non-mining areas. It was found that the contents of 7 heavy metals (As, Cd, Pb, Zn, Cu, Sn, Sb) in E. oculatus of the mining area were higher than that in the non-mining 1-11 times. The analysis of morphology shows that the external morphology, the hind wing type and the chromosomal morphology of E. oculatus are significant differences between the two populations. Based on the heavy metal accumulation，morphological change, and stable population density, it is inferred that the mining area population has been affected by heavy metals and has adapted to the environment of heavy metals pollution. Then, by analyzing the transcriptome of the two populations, it was found that the digestion, immunity, excretion, endocrine, nerve, circulation, reproductive and other systems and lysosomes, endoplasmic reticulum and other cell structure-related gene expression were suppressed. This shows that the functions of the above-mentioned related systems of E. oculatus are inhibited by heavy metal stress. However, it has also been found that through the significant up-regulation of genes related to the above system, such as ATP2B, pepsin A, ubiquitin, AQP1, ACOX, ATPeV0A, SEC61A, CANX, ALDH7A1, DLD, aceE, Hsp40, and catalase, etc., and the down-regulation of MAPK signalling pathway genes, can enhanced nutrient absorption, improve energy metabolism, repair damaged cells and degrade abnormal proteins, maintain the stability of cells and systems, and resist heavy metal damage so that E. oculatus can adapt to the environment of heavy metal pollution for a long time.

In Response to Precision Medicine: Current Subcellular Targeting Strategies for Cancer Therapy

Emerging as a potent anticancer treatment, subcellular targeted cancer therapy has drawn increasing attention, bringing great opportunities for clinical application. Here, two targeting strategies for four main subcellular organelles (mitochondria, lysosome, endoplasmic reticulum, and nucleus), including molecule- and nanomaterial (inorganic nanoparticles, micelles, organic polymers, and others)-based targeted delivery or therapeutic strategies, are summarized. Phototherapy, chemotherapy, radiotherapy, immunotherapy, and "all-in-one" combination therapy are among the strategies covered in detail. Such materials are constructed based on the specific properties and relevant mechanisms of organelles, enabling the elimination of tumors by inducing dysfunction in the corresponding organelles or destroying specific structures. The challenges faced by organelle-targeting cancer therapies are also summarized. Looking forward, a paradigm for organelle-targeting therapy with enhanced therapeutic efficacy compared to current clinical approaches is envisioned.

The transferred translocases: An old wine in a new bottle

The role of translocases was underappreciated and was not included as a separate class in the enzyme commission until August 2018. The recent research interests in proteomics of orphan enzymes, ionomics, and metallomics along with high-throughput sequencing technologies generated overwhelming data and revamped this enzyme into a separate class. This offers a great opportunity to understand the role of new or orphan enzymes in general and specifically translocases. The enzymes belonging to translocases regulate/permeate the transfer of ions or molecules across the membranes. These enzyme entries were previously associated with other enzyme classes, which are now transferred to a new enzyme class 7 (EC 7). The entries that are reclassified are important to extend the enzyme list, and it is the need of the hour. Accordingly, there is an upgradation of entries of this class of enzymes in several databases. This review is a concise compilation of translocases with reference to the number of entries currently available in the databases. This review also focuses on function as well as dysfunction of translocases during normal and disordered states, respectively.

UQCRH downregulation promotes Warburg effect in renal cell carcinoma cells

Ubiquinol-cytochrome c reductase hinge protein (UQCRH) is the hinge protein for the multi-subunit complex III of the mitochondrial electron transport chain and is involved in the electron transfer reaction between cytochrome c1 and c. Recent genome-wide transcriptomic and epigenomic profiling of clear cell renal cell carcinoma (ccRCC) by The Cancer Genome Atlas (TCGA) identified UQCRH as the top-ranked gene showing inverse correlation between DNA hypermethylation and mRNA downregulation. The function and underlying mechanism of UQCRH in the Warburg effect metabolism of ccRCC have not been characterized. Here, we verified the clinical association of low UQCRH expression and shorter survival of ccRCC patients through in silico analysis and identified KMRC2 as a highly relevant ccRCC cell line that displays hypermethylation-induced UQCRH extinction. Ectopic overexpression of UQCRH in KMRC2 restored mitochondrial membrane potential, increased oxygen consumption, and attenuated the Warburg effect at the cellular level. UQCRH overexpression in KMRC2 induced higher apoptosis and slowed down in vitro and in vivo tumor growth. UQCRH knockout by CRISPR/Cas9 had little impact on the metabolism and proliferation of 786O ccRCC cell line, suggesting the dispensable role of UQCRH in cells that have entered a Warburg-like state through other mechanisms. Together, our study suggests that loss of UQCRH expression by hypermethylation may promote kidney carcinogenesis through exacerbating the functional decline of mitochondria thus reinforcing the Warburg effect.

Defects in CISD-1, a mitochondrial iron-sulfur protein, lower glucose level and ATP production in Caenorhabditis elegans

Background

CDGSH iron sulfur domain-containing protein 1 (CISD-1) belongs to the CISD protein family that is evolutionary conserved across different species. In mammals, CISD-1 protein has been implicated in diseases such as cancers and diabetes. As a tractable model organism to study disease-associated proteins, we employed Caenorhabditis elegans in this study with an aim to establish a model for interrogating the functional relevance of CISD-1 in human metabolic conditions.

Methods

We first bioinformatically identified the human Cisd-1 homologue in worms. We then employed N2 wild-type and cisd-1(tm4993) mutant to investigate the consequences of CISD-1 loss-of-function on: 1) the expression pattern of CISD-1, 2) mitochondrial morphology pattern, 3) mitochondrial function and bioenergetics, and 4) the effects of anti-diabetes drugs.

Results

We first identified C. elegans W02B12.15 gene as the human Cisd-1 homologous gene, and pinpointed the localization of CISD-1 to the outer membrane of mitochondria. As compared with the N2 wild-type worm, cisd-1(tm4993) mutant exhibited a higher proportion of hyperfused form of mitochondria. This structural abnormality was associated with the generation of higher levels of ROS and mitochondrial superoxide but lower ATP. These physiological changes in mutants did not result in discernable effects on animal motility and lifespan. Moreover, the amount of glucose in N2 wild-type worms treated with troglitazone and pioglitazone, derivatives of TZD, was reduced to a comparable level as in the mutant animals.

Conclusions

By focusing on the Cisd-1 gene, our study established a C. elegans genetic system suitable for modeling human diabetes-related diseases.

Consequences of a Metabolic Glucose-Depletion on the Survival and the Metabolism of Cultured Rat Astrocytes

Brain astrocytes are considered to be highly glycolytic, but these cells also produce ATP via mitochondrial oxidative phosphorylation. To investigate how a metabolic depletion of glucose will affect the metabolism of astrocytes, we applied glucose at an initial concentration of 2 mM to cultured primary astrocytes and monitored the cell viability and various metabolic parameters during an incubation for up to 2 weeks. Already within 2 days of incubation the cells had completely consumed the applied glucose and lactate had accumulated in the medium to a concentration of around 3 mM. During the subsequent 10 days of incubation, the cell viability was not compromised while the extracellular lactate concentration declined to values of around 0.2 mM, before the cell viability was compromised. Application of known inhibitors of mitochondrial metabolism strongly accelerated glucose consumption and initial lactate production, while the lactate consumption was completely (antimycin A or 8-hydroxy efavirenz) and partially (efavirenz, metformin or tyrphostin 23) inhibited which caused rapid and delayed cell toxicity, respectively. The switch from glycolytic glucose metabolism to mitochondrial metabolism during the incubation was neither accompanied by alterations in the specific cytosolic lactate dehydrogenase activity or in the WST1 reduction capacity nor in the mitochondrial citrate synthase activity, but a cellular redistribution of mitochondria from a perinuclear to a more spread cytoplasmic localization was observed during the lactate consumption phase. These results demonstrate that cultured astrocytes survive a metabolism-induced glucose depletion very well by consuming lactate as fuel for mitochondrial ATP generation.

Heme Synthesis and Acquisition in Bacterial Pathogens

Bacterial pathogens require the iron-containing cofactor heme to cause disease. Heme is essential to the function of hemoproteins, which are involved in energy generation by the electron transport chain, detoxification of host immune effectors, and other processes. During infection, bacterial pathogens must synthesize heme or acquire heme from the host; however, host heme is sequestered in high-affinity hemoproteins. Pathogens have evolved elaborate strategies to acquire heme from host sources, particularly hemoglobin, and both heme acquisition and synthesis are important for pathogenesis. Paradoxically, excess heme is toxic to bacteria and pathogens must rely on heme detoxification strategies. Heme is a key nutrient in the struggle for survival between host and pathogen, and its study has offered significant insight into the molecular mechanisms of bacterial pathogenesis.

Antimycin-type depsipeptides: discovery, biosynthesis, chemical synthesis, and bioactivities

This review discusses the isolation, structural variation, biosynthesis, chemical synthesis, and biological activities of antimycin-type depsipeptides.

The Antidiabetic Drug Metformin Stimulates Glycolytic Lactate Production in Cultured Primary Rat Astrocytes

Metformin is the most frequently used drug for the treatment of type 2 diabetes in humans. However, only little is known about effects of metformin on brain metabolism. To investigate potential metabolic consequences of an exposure of brain cells to metformin, we incubated rat astrocyte-rich primary cultures with this compound. Metformin in concentrations of up to 30 mM did not acutely compromise the viability of astrocytes, but caused a time- and concentration-dependent increase in cellular glucose consumption and lactate production. For acute incubations in the hour range, the presence of 10 mM metformin doubled the glycolytic flux, while already 1 mM metformin doubled glycolytic flux during incubation for 24 h. In addition to metformin, also other guanidino compounds increased astrocytic lactate production. After 4 h of incubation, half-maximal stimulation of glycolysis was observed for metformin, guanidine and phenformin at concentrations of around 3 mM, 3 mM and 30 µM, respectively. The acute stimulation of glycolytic lactate production by metformin was persistent after removal of extracellular metformin and was also observed, if glucose was absent from the incubation medium or replaced by other hexoses. The metformin-induced stimulation of glycolytic flux was not prevented by compound C, an inhibitor of AMP-dependent protein kinase, nor was it additive to the stimulation of glycolytic flux caused by respiratory chain inhibitors. These data demonstrate that the antidiabetic drug metformin has the potential to strongly activate glycolytic lactate production in brain astrocytes.

Crossed and linked histories of tetrapyrrolic macrocycles and their use for engineering pores within sol-gel matrices

The crossed and linked histories of tetrapyrrolic macrocycles, interwoven with new research discoveries, suggest that Nature has found in these structures a way to ensure the continuity of life. For diverse applications porphyrins or phthalocyanines must be trapped inside solid networks, but due to their nature, these compounds cannot be introduced by thermal diffusion; the sol-gel method makes possible this insertion through a soft chemical process. The methodologies for trapping or bonding macrocycles inside pristine or organo-modified silica or inside ZrO₂ xerogels were developed by using phthalocyanines and porphyrins as molecular probes. The sizes of the pores formed depend on the structure, the cation nature, and the identities and positions of peripheral substituents of the macrocycle. The interactions of the macrocyclic molecule and surface Si-OH groups inhibit the efficient displaying of the macrocycle properties and to avoid this undesirable event, strategies such as situating the macrocycle far from the pore walls or to exchange the Si-OH species by alkyl or aryl groups have been proposed. Spectroscopic properties are better preserved when long unions are established between the macrocycle and the pore walls, or when oligomeric macrocyclic species are trapped inside each pore. When macrocycles are trapped inside organo-modified silica, their properties result similar to those displayed in solution and their intensities depend on the length of the alkyl chain attached to the matrix. These results support the prospect of tuning up the pore size, surface area, and polarity inside the pore cavities in order to prepare efficient catalytic, optical, sensoring, and medical systems. The most important feature is that research would confirm again that tetrapyrrolic macrocycles can help in the development of the authentic pore engineering in materials science.

Amplification of the UQCRFS1 Gene in Gastric Cancers

Purpose

The specific aim of this study is to unravel a DNA copy number alterations, and to search for novel genes that are associated with the development of Korean gastric cancer.

Materials and Methods

We investigated a DNA copy number changes in 23 gastric adenocarcinomas by array-comparative genomic hybridization and quantitative real-time polymerase chain reaction analyses. Besides, the expression of UQCRFS1, which shows amplification in array-CGH, was examined in 186 gastric cancer tissues by an immunohistochemistry, and in 9 gastric cancer cell lines, as well as 24 gastric cancer tissues by immunoblotting.

Results

We found common gains at 48 different loci, and a common loss at 19 different loci. Amplification of UQCRFS1 gene at 19q12 was found in 5 (21.7%) of the 23 gastric cancers in an array-comparative genomic hybridization and DNA copy number were increased in 5 (20.0%) out of the 25 gastric cancer in quantitative real-time polymerase chain reaction. In immunohistochemistry, the overexpression of the protein was detected in 105 (56.5%) out of the 186 gastric cancer tissues. Statistically, there was no significant relationship between the overexpression of UQCRFS1 and clinicopathologic parameters (P>0.05). In parallel, the overexpression of UQCRFS1 protein was confirmed in 6 (66.7%) of the 9 gastric cancer cell lines, and 12 (50.0%) of the 24 gastric cancer tissues by immunoblotting.

Conclusions

These results suggest that the overexpression of UQCRFS1 gene may contribute to the development and/or progression of gastric cancer, and further supported that mitochondrial change may serve as a potential cancer biomarker.

Classical and alternative components of the mitochondrial respiratory chain in pathogenic fungi as potential therapeutic targets

The frequency of opportunistic fungal infection has increased drastically, mainly in patients who are immunocompromised due to organ transplant, leukemia or HIV infection. In spite of this, only a few classes of drugs with a limited array of targets, are available for antifungal therapy. Therefore, more specific and less toxic drugs with new molecular targets is desirable for the treatment of fungal infections. In this context, searching for differences between mitochondrial mammalian hosts and fungi in the classical and alternative components of the mitochondrial respiratory chain may provide new potential therapeutic targets for this purpose.

Leptin modulated changes in adipose tissue protein expression in ob/ob mice

Comparative proteomic analyses were performed in adipose tissue of leptin-deficient ob/ob mice treated with leptin or control buffer in order to identify the protein expression changes as the potential targets of leptin. Mice were treated with either phosphate-buffered saline (control) or 10 µg/day leptin for 14 days via subcutaneous osmotic minipumps. Total protein from white adipose tissue was extracted and labeled with different fluorescent cyanine dyes for analysis by two-dimensional difference gel electrophoresis (DIGE). Spots that were differentially expressed and appeared to have sufficient material for mass spectrometry analysis were picked and digested with trypsin and subjected to MALDI-TOF MS for protein identification. Twelve functional protein groups were found differentially expressed in adipose tissue of leptin-treated vs. control ob/ob mice, including molecular chaperones and redox proteins such as calreticulin (CALR), protein disulfide isomerase-associated 3 (PDIA3), prohibitin (PHB), and peroxiredoxin-6 (PRDX6); cytoskeleton proteins such as β actin, desmin, and α-tubulin; and some other proteins. The mRNA levels of CALR, PDIA3, and PHB were measured by real-time reverse transcription-PCR and found to be upregulated (P < 0.05), consistent with the fold change in protein expression level. Our findings suggest that leptin's effects on lipid metabolism and apoptosis may be mediated in part by alterations in expression of molecular chaperones and redox proteins for regulating endoplasmic reticulum stress and cytoskeleton proteins for regulating mitochondrial morphology.

Spectrally distinct cytochrome b-563 components in a chloroplast cytochrome b-f complex: Interaction with a hydroxyquinoline N-oxide

The two heme equivalents of cytochrome b-563 in the photosynthetic cytochrome b-f complex can be distinguished by their rate of reduction with dithionite at 25 degrees C and by their optical absorption spectra at 77 K. The cytochrome b component that is rapidly reduced after addition of dithionite or reduced ferredoxin possesses an alpha band that splits at 77 K into two peaks, at 557 and 561 nm. Prolonged incubation with reductant reveals a second, approximately equimolar cytochrome b component that has at 77 K an unsplit alpha-band maximum at 561 nm. The designations cytochrome b-563(H) and cytochrome b-563(L), respectively, are proposed for the rapidly and more slowly reduced cytochrome b-563 components. Potentiometric titration establishes a midpoint potential, E(m), of -30 mV (electron change n approximately 2) for cytochrome b-563(H) and -150 mV (n = 1) for cytochrome b-563(L) at pH 7.5. The reduction potential of these components is raised by 2-heptyl-4-hydroxyquinoline N-oxide, giving E(m) values of +57 and -34 mV, respectively, with each titration slope approximating n = 2.

Photooxidation of the high-potential iron-sulfur center in chloroplasts

The high-potential iron-sulfur center associated with the g = 1.89-1.90 electron paramagnetic resonance signal in spinach chloroplasts is fully reduced in the dark. It is photooxidized in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea and reduced after illumination with red actinic light in the absence of inhibitors. The light-induced redox changes of the high-potential iron-sulfur center are shown to correlate with those of plastocyanin detected at g = 2.05. Demonstration of light-induced redox changes in the high-potential iron-sulfur center provides support for a functional role of this component in the chloroplast electron transport chain.

Dinitrosyl iron complexes relevant to Rieske cluster nitrosylation

Reaction of the Rieske cluster model complex (Et(4)N)(2)[(N(2)CHPh)Fe(2)S(2)(S(2)-o-xyl)] (N(2)CHPh = dianion of 2,2'-(phenylmethylene)bis(3-methylindole); S(2)-o-xyl = dianion of 1,2-phenylenedimethanethiol) with nitric oxide results in disassembly of the iron-sulfur core and formation of {Fe(NO)(2)}(9) dinitrosyliron complexes (DNICs). Isolation and characterization of these DNICs, including the new compound, (Et(4)N)[(N(2)CHPh)Fe(NO)(2)], demonstrates a homology between the synthetic Riekse cluster and purely thiolate-bound Fe(2)S(2) clusters in reactions involving NO. To model the nitrogen-rich environment of Rieske cluster-derived dinitroysliron species, a new type of neutral {Fe(NO)(2)}(9) DNIC was prepared containing a beta-diketiminate ligand. One-electron reduction of this compound affords the isolable {Fe(NO)(2)}(10) DNIC. These compounds represent a rare example of structurally analogous DNIC redox partners.

A structural perspective on mechanism and function of the cytochrome bc (1) complex

The cytochrome bc (1) complex is a fundamental component of the energy conversion machinery of respiratory and photosynthetic electron transfer chains. The multi-subunit membrane protein complex couples electron transfer from hydroquinone to cytochrome c to the translocation of protons across the membrane, thereby substantially contributing to the proton motive force that is used for ATP synthesis. Considerable progress has been made with structural and functional studies towards complete elucidation of the Q cycle mechanism, which was originally proposed by Mitchell 30 years ago. Yet, open questions regarding key steps of the mechanism still remain. The role of the complex as a major source of reactive oxygen species and its implication in pathophysiological conditions has recently gained interest.

Mitochondrial alterations in human gastric carcinoma cell line

We compared mitochondrial function, morphology, and proteome in the rat normal gastric cell line RGM-1 and the human gastric cancer cell line AGS. Total numbers and cross-sectional sizes of mitochondria were smaller in AGS cells. Mitochondria in AGS cells were deformed and consumed less oxygen. Confocal microscopy indicated that the mitochondrial inner membrane potential was hyperpolarized and the mitochondrial Ca(2+) concentration was elevated in AGS cells. Interestingly, two-dimensional electrophoresis proteomics on the mitochondria-enriched fraction revealed high expression of four mitochondrial proteins in AGS cells: ubiquinol-cytochrome c reductase, mitochondrial short-chain enoyl-coenzyme A hydratase-1, heat shock protein 60, and mitochondria elongation factor Tu. The results provide clues as to the mechanism of the mitochondrial changes in cancer at the protein level and may serve as potential cancer biomarkers in mitochondria.

Inhibition of Mitochondrial Respiration as a Source of Adaphostin-induced Reactive Oxygen Species and Cytotoxicity

Adaphostin is a dihydroquinone derivative that is undergoing extensive preclinical testing as a potential anticancer drug. Previous studies have suggested that the generation of reactive oxygen species (ROS) plays a critical role in the cytotoxicity of this agent. In this study, we investigated the source of these ROS. Consistent with the known chemical properties of dihydroquinones, adaphostin simultaneously underwent oxidation to the corresponding quinone and generated ROS under aqueous conditions. Interestingly, however, this quinone was not detected in intact cells. Instead, high performance liquid chromatography demonstrated that adaphostin was concentrated by up to 300-fold in cells relative to the extracellular medium and that the highest concentration of adaphostin (3000-fold over extracellular concentrations) was detected in mitochondria. Consistent with a mitochondrial site for adaphostin action, adaphostin-induced ROS production was diminished by >75% in MOLT-4 rho(0) cells, which lack mitochondrial electron transport, relative to parental MOLT-4 cells. In addition, inhibition of oxygen consumption was observed when intact cells were treated with adaphostin. Loading of isolated mitochondria to equivalent adaphostin concentrations caused inhibition of uncoupled oxygen consumption in mitochondria incubated with the complex I substrates pyruvate and malate or the complex II substrate succinate. Further analysis demonstrated that adaphostin had no effect on pyruvate or succinate dehydrogenase activity. Instead, adaphostin inhibited reduced decylubiquinone-induced cytochrome c reduction, identifying complex III as the site of inhibition by this agent. Moreover, adaphostin enhanced the production of ROS by succinate-charged mitochondria. Collectively, these observations demonstrate that mitochondrial respiration rather than direct redox cycling of the hydroquinone moiety is a source of adaphostin-induced ROS and identify complex III as a potential target for antineoplastic agents.

Mitoenergetic failure in Alzheimer disease

Brain cells are highly energy dependent for maintaining ion homeostasis during high metabolic activity. During active periods, full mitochondrial function is essential to generate ATP from electrons that originate with the oxidation of NADH. Decreasing brain metabolism is a significant cause of cognitive abnormalities of Alzheimer disease (AD), but it remains uncertain whether this is the cause of further pathology or whether synaptic loss results in a lower energy demand. Synapses are the first to show pathological symptoms in AD before the onset of clinical symptoms. Because synaptic function has high energy demands, interruption in mitochondrial energy supply could be the major factor in synaptic failure in AD. A newly discovered age-related decline in neuronal NADH and redox ratio may jeopardize this function. Mitochondrial dehydrogenases and several mutations affecting energy transfer are frequently altered in aging and AD. Thus, with the accumulation of genetic defects in mitochondria at the level of energy transfer, the issue of neuronal susceptibility to damage as a function of age and age-related disease becomes important. In an aging rat neuron model, mitochondria are both chronically depolarized and produce more reactive oxygen species with age. These concepts suggest that multiple treatment targets may be needed to reverse this multifactorial disease. This review summarizes new insights based on the interaction of mitoenergetic failure, glutamate excitotoxicity, and amyloid toxicity in the exacerbation of AD.

2-n-nonyl-4-hydroxy[3-3H]quinoline N-oxide: interaction with the mitochondrial membrane

1. Synthesized 2-n-nonyl-4-hydroxy[3-3H]quinoline N-oxide ([3H]NoHOQnO) is a powerful inhibitor of both NADH oxidase and succinate oxidase activities in submitochondrial particles from beef heart. 2. The binding of [3H]NoHOQnO to submitochondrial particles reveals one specific binding site, which is sensitive to antimycin, and a large amount of aspecific binding. 3. The content of [3H]NoHOQnO-specific binding sites is related to the cytochrome b content in the particles. 4. The binding of [3H]NoHOQnO to the specific site causes the inhibition of electron transfer. 5. The relation between the inhibition of NADH oxidation and [3H]NoHOQnO-specific binding is hyperbolic.

Ubiquinol cytochrome c reductase (UQCRFS1) gene amplification in primary breast cancer core biopsy samples

OBJECTIVES

The ubiquinol cytochrome c reductase UQCRFS1 is a key subunit of the cytochrome bc1 complex (complex III) of the mitochondrial respiratory chain. The purpose of this study is to evaluate the significance of the ubiquinol cytochrome c reductase UQCRFS1 gene amplification in primary breast cancers.

METHODS

Samples were obtained from image-guided core needle biopsies (CNB) in 40 patients with nontreated breast cancers. To examine UQCRFS1 gene amplification, we employed fluorescent in situ hybridization using BACs RP11-46I12 that harbors UQCRFS1 gene, RP11-110J19 that overlaps to RP11-46I12, and CA125 as a control gene. The amplification data were evaluated blindly of histopathological factors.

RESULTS

Amplification of UQCRFS1 gene was found in 5 of 39 specimens (12.8%). The specimens with amplified UQCRFS1 gene were associated with high grade of cancer cells (P = 0.005).

CONCLUSIONS

These results suggest that the UQCRFS1 gene appears to be involved in development of more aggressive phenotype of breast cancer.

Role of ALDP (ABCD1) and mitochondria in X-linked adrenoleukodystrophy

Peroxisomal disorders have been associated with malfunction of peroxisomal metabolic pathways, but the pathogenesis of these disorders is largely unknown. X-linked adrenoleukodystrophy (X-ALD) is associated with elevated levels of very-long-chain fatty acids (VLCFA; C(>22:0)) that have been attributed to reduced peroxisomal VLCFA beta-oxidation activity. Previously, our laboratory and others have reported elevated VLCFA levels and reduced peroxisomal VLCFA beta-oxidation in human and mouse X-ALD fibroblasts. In this study, we found normal levels of peroxisomal VLCFA beta-oxidation in tissues from ALD mice with elevated VLCFA levels. Treatment of ALD mice with pharmacological agents resulted in decreased VLCFA levels without a change in VLCFA beta-oxidation activity. These data indicate that ALDP does not determine the rate of VLCFA beta-oxidation and that VLCFA levels are not determined by the rate of VLCFA beta-oxidation. The rate of peroxisomal VLCFA beta-oxidation in human and mouse fibroblasts in vitro is affected by the rate of mitochondrial long-chain fatty acid beta-oxidation. We hypothesize that ALDP facilitates the interaction between peroxisomes and mitochondria, resulting, when ALDP is deficient in X-ALD, in increased VLCFA accumulation despite normal peroxisomal VLCFA beta-oxidation in ALD mouse tissues. In support of this hypothesis, mitochondrial structural abnormalities were observed in adrenal cortical cells of ALD mice.

Structure and function of cytochrome bc complexes

The cytochrome bc complexes represent a phylogenetically diverse group of complexes of electron-transferring membrane proteins, most familiarly represented by the mitochondrial and bacterial bc1 complexes and the chloroplast and cyanobacterial b6f complex. All these complexes couple electron transfer to proton translocation across a closed lipid bilayer membrane, conserving the free energy released by the oxidation-reduction process in the form of an electrochemical proton gradient across the membrane. Recent exciting developments include the application of site-directed mutagenesis to define the role of conserved residues, and the emergence over the past five years of X-ray structures for several mitochondrial complexes, and for two important domains of the b6f complex.

Ubiquinol:cytochrome c oxidoreductase. Effects of inhibitors on reverse electron transfer from the iron-sulfur protein to cytochrome b

The effects of inhibitors on the reduction of the bis-heme cytochrome b of ubiquinol: cytochrome c oxidoreductase (complex III, bc1 complex) has been studied in bovine heart submitochondrial particles (SMP) when cytochrome b was reduced by NADH and succinate via the ubiquinone (Q) pool or by ascorbate plus N,N,N', N'-tetramethyl-p-phenylenediamine via cytochrome c1 and the iron-sulfur protein of complex III (ISP). The inhibitors used were antimycin (an N-side inhibitor), beta-methoxyacrylate derivatives, stigmatellin (P-side inhibitors), and ethoxyformic anhydride, which modifies essential histidyl residues in ISP. In agreement with our previous findings, the following results were obtained: (i) When ISP/cytochrome c1 were prereduced or SMP were treated with a P-side inhibitor, the high potential heme bH was fully and rapidly reduced by NADH or succinate, whereas the low potential heme bL was only partially reduced. (ii) Reverse electron transfer from ISP/c1 to cytochrome b was inhibited more by antimycin than by the P-side inhibitors. This reverse electron transfer was unaffected when, instead of normal SMP, Q-extracted SMP containing 200-fold less Q (0. 06 mol Q/mol cytochrome b or c1) were used. (iii) The cytochrome b reduced by reverse electron transfer through the leak of a P-side inhibitor was rapidly oxidized upon subsequent addition of antimycin. This antimycin-induced reoxidation did not happen when Q-extracted SMP were used. The implications of these results on the path of electrons in complex III, on oxidant-induced extra cytochrome b reduction, and on the inhibition of forward electron transfer to cytochrome b by a P-side plus an N-side inhibitor have been discussed.

On the mechanism of quinol oxidation in the bc1 complex

The question of whether significant levels of a semiquinone can be generated in the Qo site of the bc1 complex under conditions of oxidant-induced reduction is relevant to the mechanism of bifurcation of electron transfer in this site. It has already been reported that beef heart submitochondrial particles under such conditions exhibit an EPR-detectable semiquinone, which is distinct from Q-i and which was attributed to a semiquinone in the Qo site (de Vries, S., Albracht, S. P. J., Berden, J. A., and Slater, E. C. (1981) J. Biol. Chem. 256, 11996-11998). However, we show here that this signal, which can be generated to a level of around 0.1 per bc1 monomer, is insensitive to the Qo site inhibitors myxothiazol, E-beta-methoxyacrylate-stilbene, and stigmatellin, indicating that it does not arise from a Q-o species. Based on sensitivities to inhibitors of other Q sites, up to 60% of the signal may arise from semiquinones of complexes I and II. We further show that the iron-sulfur center remains EPR silent under oxidant-induced reduction conditions. Overall, the results indicate that, under conditions of oxidant-induced reduction, the Qo site is occupied primarily by quinol with the iron-sulfur center oxidized, or, possibly, by an antiferromagnetically coupled semiquinone/reduced iron-sulfur center pair, which are EPR silent. This is discussed in relation to proposed mechanisms of quinol oxidation in the Qo site, and we describe a minimal intermediate-controlled bifurcation model based on rate constants by which bifurcated electron transfer at the Qo site might occur.

An antibiotic, ascofuranone, specifically inhibits respiration and in vitro growth of long slender bloodstream forms of Trypanosoma brucei brucei

Ascofuranone, a prenylphenol antibiotic isolated from a phytopathogenic fungus, Ascochyta visiae, strongly inhibited both glucose-dependent cellular respiration and glycerol-3-phosphate-dependent mitochondrial O2 consumption of long slender bloodstream forms of Trypanosoma brucei brucei. This inhibition was suggested to be due to inhibition of the mitochondrial electron-transport system, composed of glycerol-3-phosphate dehydrogenase (EC 1.1.99.5) and plant-like alternative oxidase. Ascofuranone noncompetitively inhibited the reduced coenzyme Q1-dependent O2 uptake of the mitochondria with respect to ubiquinol (Ki = 2.38 nM). Therefore, the susceptible site is deduced to be the ubiquinone redox machinery which links the two enzyme activities. Further, ascofuranone in combination with glycerol completely blocked energy production, and potently inhibited the in vitro growth of the parasite. Our findings suggest that ascofuranone might be a promising candidate for the chemotherapeutic agents of African trypanosomiasis.

An antibiotic, ascofuranone, specifically inhibits respiration and in vitro growth of long slender bloodstream forms of Trypanosoma brucei brucei

Ascofuranone, a prenylphenol antibiotic isolated from a phytopathogenic fungus, Ascochyta visiae, strongly inhibited both glucose-dependent cellular respiration and glycerol-3-phosphate-dependent mitochondrial O2 consumption of long slender bloodstream forms of Trypanosoma brucei brucei. This inhibition was suggested to be due to inhibition of the mitochondriai electron-transport system, composed of glycerol-3-phosphate dehydrogenase (EC 1.1.99.5) and plant-like alternative oxidase. Ascofuranone noncompetitively inhibited the reduced coenzyme Q1-dependent O2 uptake of the mitochondria with respect to ubiquinol (Ki = 2.38 nM). Therefore, the susceptible site is deduced to be the ubiquinone redox machinery which links the two enzyme activities. Further, ascofuranone in combination with glycerol completely blocked energy production, and potently inhibited the in vitro growth of the parasite. Our findings suggest that ascofuranone might be a promising candidate for the chemotherapeutic agents of African trypanosomiasis.

[3H]dihydrorotenone binding to NADH: ubiquinone reductase (complex I) of the electron transport chain: an autoradiographic study

Abnormalities of mitochondrial energy metabolism may play a role in normal aging and certain neurodegenerative disorders. In this regard, complex I of the electron transport chain has received substantial attention, especially in Parkinson's disease. The conventional method for studying complex I has been quantitation of enzyme activity in homogenized tissue samples. To enhance the anatomic precision with which complex I can be examined, we developed an autoradiographic assay for the rotenone site of this enzyme. [3H]dihydrorotenone ([3H]DHR) binding is saturable (KD = 15-55 nM) and specific, and Hill slopes of 1 suggest a single population of binding sites. Nicotinamide adenine dinucleotide (NADH) enhances binding 4- to 80-fold in different brain regions (EC50 = 20-40 microM) by increasing the density of recognition sites (Bmax). Nicotinamide adenine dinucleotide phosphate also increases binding, but NAD+ does not. In skeletal muscle, heart, and kidney, binding was less affected by NADH. [3H]DHR binding is inhibited by rotenone (IC50 = 8-20 nM), meperidine (IC50 = 34-57 microM), amobarbitol (IC50 = 375-425 microM), and MPP+ (IC50 = 4-5 mM), consistent with the potencies of these compounds in inhibiting complex I activity. Binding is heterogeneously distributed in brain with the density in gray matter structures varying more than 10-fold. Lesion studies suggest that a substantial portion of binding is associated with nerve terminals. [3H]DHR autoradiography is the first quantitative method to examine complex I with a high degree of anatomic precision. This technique may help to clarify the potential role of complex I dysfunction in normal aging and disease.

Structure, sequence and location of the UQCRFS1 gene for the human Rieske Fe-S protein

We have identified and studied the chromosomal location of the human Rieske Fe-S protein-encoding gene UQCRFS1. Mapping by hybridization to a panel of monochromosomal hybrid cell lines indicated that a UQCRFS1 partial cDNA was derived from either chromosome 19 or 22. By screening a human chromosome 19 specific genomic cosmid library with a probe from this cDNA sequence, we identified a corresponding cosmid. Portions of this cosmid were sequenced directly. The exon, exon:intron junction and flanking sequences verified that this cosmid contains the genomic locus. Fluorescent in situ hybridization (FISH) was performed to localize this cosmid to chromosome band 19q12.

Structural factors of antimycin A molecule required for inhibitory action

A series of antimycin A analogues was synthesized by modifying the salicylic acid moiety, whereas the portion of the molecule corresponding to the natural dilactone-ring moiety was fixed as di-n-octyl L-glutamate. To probe the structure of the antimycin A binding site, the structural factors of the salicylic acid moiety required for inhibitory action were examined by means of structure-activity studies with intact rat-liver mitochondria and the cytochrome bc1 complex isolated from bovine heart mitochondria. As suggested earlier (Rieske, J.S. (1976) Biochim. Biophys. Acta 456, 195-247), the phenolic OH was very important for inhibition. For the derivatives which do not possess a formylamino group in the 3-position (ortho to the phenolic OH), the inhibitory activity tended to increase as the electron-withdrawing property of the substituent increased, i.e., as the acidity of the phenolic OH group increased. This indicates that the acidity of the phenolic OH is an important factor governing inhibition. While the electron-withdrawing property of the formylamino group itself is rather poor, 3-formylamino derivatives elicited potent activity. The conformation of the 3-formylamino group was also found to be a very important factor in establishing inhibitory activity. In addition, the bulkier the moiety corresponding to the 3-formylamino group, the lower the activity. These results demonstrate that the presence of the 3-formylamino group, and its proper conformation, are needed for a close fitting of antimycin A to its binding domain. Although the inhibitors that lack a 3-formylamino group retained fairly potent activity, their effects on the reduction of cytochromes b and c1 were somewhat different from those of natural antimycin A, indicating that the 3-formylamino group is essential for inhibitor binding to the cytochrome bc1 complex in the same manner as natural antimycin A. It is concluded that both the 3-formylamino group and the phenolic OH of antimycin A make important contributions to specific interactions with the amino acid residues of the cytochrome b.

Analysis of revertants from respiratory deficient mutants within the center N of cytochrome b in Saccharomyces cerevisiae

Four modified cytochrome b's carrying mononucleotide substitutions affecting center N residues were analysed. The mutant carrying a G33D change does not incorporate heme into the apocytochrome b and fails to grow on non-fermentable carbon sources. Out of 85 genetically independent revertants derived from this mutant, 82 were true back-mutants restoring the wild type sequence (D33G). The remaining three replaced the aspartic acid by an alanine (D33A) indicating that small size residues are best tolerated at this position which is consistent with the perfect conservation of the G33 during evolution. This glycine may be of crucial importance for helix packing around the hemes. The replacement of methionine at position 221 by lysine (M221K) produced a non-functional cytochrome b [(1993) J. Biol. Chem. 268, 15626-15632]. Non-native revertants replacing the lysine 221 by glutamic acid (K221E) or glutamine (K221Q) expressed a selective resistance to antimycin and antimycin derivatives having a modified dilactone ring moiety. Cytochrome b residues in 33 and in 221 seemed to contribute to the quinone reduction (QN) site of the cytochrome bc1 complex. Possible intramolecular interactions between the N-terminal region and the loop connecting helices IV and V of cytochrome b are proposed.

Mutational analysis of assembly and function of the iron-sulfur protein of the cytochrome bc1 complex in Saccharomyces cerevisiae

The iron-sulfur protein of the cytochrome bc1 complex oxidizes ubiquinol at center P in the protonmotive Q cycle mechanism, transferring one electron to cytochrome c1 and generating a low-potential ubisemiquinone anion which reduces the low-potential cytochrome b-566 heme group. In order to catalyze this divergent transfer of two reducing equivalents from ubiquinol, the iron-sulfur protein must be structurally integrated into the cytochrome bc1 complex in a manner which facilitates electron transfer from the iron-sulfur cluster to cytochrome c1 and generates a strongly reducing ubisemiquinone anion radical which is proximal to the b-566 heme group. This radical must also be sequestered from spurious reactivities with oxygen and other high-potential oxidants. Experimental approaches are described which are aimed at understanding how the iron-sulfur protein is inserted into center P, and how the iron-sulfur cluster is inserted into the apoprotein.

Mitochondrial ubiquinol-cytochrome c reductase complex: crystallization and protein: ubiquinone interaction

The ubiquinol-cytochrome c reductase complex was crystallized in a thin plate form, which diffracts X-rays to 7 A resolution in the presence of mother liquor. This crystalline complex contains ten protein subunits and 140 nmol phospholipid per milligram protein. Over 90% of the phospholipid and ubiquinone in the reductase can be removed by repeated ammonium sulfate precipitation in the presence of 0.5% sodium cholate. The delipidated complex has no enzymatic activity and shows significant changes in the circular dichroism spectrum in the near UV region and in the EPR characteristics of both cytochromes b. Enzyme activity and spectral characteristics can be restored by replenishing the phospholipid and ubiquinone. The structural requirements of ubiquinone for electron transport were studied by measuring the ability of a variety of synthetic ubiquinone derivatives to restore the enzymatic activity and native spectroscopic signatures to the delipidated complex. Q-binding proteins and binding domains were identified using photoaffinity labeled Q-derivatives and HPLC separation of photolabeled peptides. Interaction between ubiquinol-cytochrome c reductase and succinate-Q reductase was established by differential scanning calorimetry and saturation transfer EPR using spin-labeled ubiquinol-cytochrome c reductase. Involvement of iron-sulfur protein in proton translocation by ubiquinol-cytochrome c reductase was investigated by hematorporphyrin-promoted photoinactivation of the complex. The cDNAs encoding the Rieske iron-sulfur protein and a small molecular mass Q-binding protein (QPc-9.5 kDa) were isolated and their nucleotide sequences determined. These will be useful in future structural and mechanistic studies of ubiquinol-cytochrome c reductase via in vitro reconstitution between an over-expressed, mutated subunit and a specific subunit-depleted reductase.

Inhibition of electron transport of rat-liver mitochondria by synthesized antimycin A analogs

A series of antimycin A analogs was synthesized by replacement of a dilactone-ring moiety of natural antimycin A by various alkyl, substituted phenyl, substituted diphenyl ether, or amino acid ester groups. The structure-inhibitory activity relationship was studied with rat-liver mitochondria to identify roles of the dilactone-ring moiety in the inhibitor binding to a Qi reaction center of cytochrome bc1 complex. All derivatives caused further reduction of cytochrome b reduced by succinate and the oxidant-induced reduction, showing that the derivatives inhibited electron transport by interacting with a Qi reaction center. The inhibition tended to increase as the hydrophobicity of the inhibitor increased. The mode of binding of inhibitor molecules to a Qi center, which was reflected in, for example, a sigmoidal titration curve for respiratory inhibition and a time-dependent change in inhibitory activity, varied depending on structure. These results suggested that the role of the dilactone-ring moiety of antimycin A may be not only to support hydrophobic interaction with the binding domain by increasing the hydrophobicity of the molecule, as proposed earlier, but also to regulate close fitting of the salicylic acid moiety to the binding domain.

Comparison between the properties of 3-nitrosalicyl-N-alkylamide and antimycin A acting on QH2:cytochrome c reductase

3-Nitrosalicyl N-alkylamide was found to be an inhibitor different from antimycin A not only in its inhibitory nature but also in many other aspects. This difference indicated that the 11 kDa component, which was identified as the antimycin A (AA) binding factor in the QH2: cytochrome c reductase of Rhodopseudomonas sphaeroides by Wilson et al. ((1985) J. Biol. Chem. 260, 10288-10292) using the radioactive photoaffinity analogue 3-azidosalicyl N-octadecylamide, was not the genuine binding site of AA. Based on the observations that the 3-azidosalicyl N-alkylamide specifically inhibits the reactions of ubiquinone catalyzed by Q-related enzymes of the respiratory chain, the labeled 11 kDa factor might be one of the ubiquinone binding proteins in QH2:cytochrome c reductase.

Cytochrome bc 1 and b 6 f complexes of photosynthetic membranes

All photosynthetic membranes contain a cytochrome bc 1 or b 6 f complex that catalyzes the oxidation of quinols and the reduction of a high-potential electron carrier, such as cytochrome c 2 or plastocyanin. The cytochrome complex also functions in the translocation of protons across the membrane and as a consequence, establishes the proton motive force that is used for the synthesis of ATP. The structure and function of the cytochrome complexes are first reviewed in this chapter. Amino acid sequence information for almost all of the protein subunits of these complexes is now available, and these allow for a detailed consideration of functional domains in the protein subunits and for a further discussion of the evolution of the cytochrome complex in photosynthetic organisms.

Functional analysis in yeast of cDNA coding for the mitochondrial Rieske iron-sulfur protein of higher plants

cDNA clones coding for the nuclear-encoded mitochondrial Rieske iron-sulfur protein (RISP) have been isolated from maize and tobacco. Complementation analysis of hybrid proteins consisting of different domains of plant and yeast RISPs showed that the carboxyl two-thirds of the plant protein is functionally equivalent to that of the yeast protein. The amino terminus of the RISP, however, seems to be species specific because this region is not interchangeable between plant and yeast proteins. Complementation analysis of hybrid proteins also identified a structurally conserved domain probably essential for the function of bc1 complex RISPs. A specific domain from the plant RISP was found to cause temperature-sensitive respiratory growth in yeast. We have demonstrated that yeast can serve as a model system to study the structural and functional relationships of plant gene products that are enzymatic components of the mitochondrial respiratory chain.

Immunochemical study of subunit VI (Mr 13,400) of mitochondrial ubiquinol-cytochrome c reductase

A preparation containing the Mr 13,400 protein (subunit VI), phospholipid, and ubiquinone was isolated from bovine heart mitochondrial ubiquinol-cytochrome c reductase by a procedure involving Triton X-100 and urea solubilization, calcium phosphate-cellulose column chromatography at different pHs, acetone precipitation, and decanoyl-N-methylglucamide-sodium cholate extraction. The protein in this preparation corresponds to subunit VI of ubiquinol-cytochrome c reductase resolved in the sodium dodecyl sulfate-polyacrylamidce gel electrophoresis system of Schägger et al. (1987, FEBS Lett. 21, 161-168) and has the same amino acid sequence as that of the Mr 13,400 protein reported by Wakabayashi et al. (1985, J. Biol. Chem. 260, 337-343). The phospholipid and ubiquinone present in the preparation copurify with but are not intrinsic components of, the Mr 13,400 protein. This preparation has a potency and behavior identical to that of a free phospholipid preparation in restoring activity to delipidated ubiquinol-cytochrome c reductase. Antibodies against Mr 13,400 react only with Mr 13,400 protein and complexes which contain it. They do not inhibit intact, lipid-sufficient ubiquinol-cytochrome c reductase. However, when delipidated ubiquinol-cytochrome c reductase is incubated with antibodies prior to reconstitution with phospholipid, a 55% decrease in the restoration activity is observed, indicating that the catalytic site-related epitopes of the Mr 13,400 protein are buried in the phospholipid environment. Antibodies against Mr 13,400 cause an increase of apparent Km for ubiquinol-2 in ubiquinol-cytochrome c reductase. When mitoplasts or submitochondrial particles are exposed to a horseradish peroxidase conjugate of the Fab' fragment of anti-Mr 13,400 antibodies, peroxidase activity is found mainly in the submitochondrial particles preparation; little activity is detected in mitoplasts. This suggests that the Mr 13,400 protein is extruded toward the matrix side of the membrane.

Electron spin echo envelope modulation spectroscopy supports the suggested coordination of two histidine ligands to the Rieske Fe-S centers of the cytochrome b6f complex of spinach and the cytochrome bc1 complexes of Rhodospirillum rubrum, Rhodobacter sphaeroides R-26, and bovine heart mitochondria

Electron spin echo envelope modulation (ESEEM) experiments performed on the Rieske Fe-S clusters of the cytochrome b6f complex of spinach chloroplasts and of the cytochrome bc1 complexes of Rhodospirillum rubrum, Rhodobacter sphaeroides R-26, and bovine heart mitochondria show modulation components resulting from two distinct classes of 14N ligands. At the g = 1.92 region of the Rieske EPR spectrum of the cytochrome b6f complex, the measured hyperfine couplings for the two classes of coupled nitrogens are A1 = 4.6 MHz and A2 = 3.8 MHz. Similar couplings are observed for the Rieske centers in the three cytochrome bc1 complexes. These ESEEM results indicate a nitrogen coordination environment for these Rieske Fe-S centers that is similar to that of the Fe-S cluster of a bacterial dioxygenase enzyme with two coordinated histidine ligands [Gurbiel, R. J., Batie, C. J., Sivaraja, M., True, A. E., Fee, J. A., Hoffman, B. M., & Ballou, D. P. (1989) Biochemistry 28, 4861-4871]. The Rieske Fe-S cluster lacks modulation components from a weakly coupled peptide nitrogen observed in water-soluble spinach ferredoxin. Treatment with the quinone analogue inhibitor DBMIB causes a shift in the Rieske EPR spectrum to g = 1.95 with no alteration in the magnetic coupling to the two nitrogen atoms. However, the ESEEM pattern of the DBMIB-altered Rieske EPR signal shows evidence of an additional weakly coupled nitrogen similar to that observed in the spinach ferredoxin ESEEM patterns.

Glycine-231 residue of the mouse mitochondrial protonmotive cytochrome b: mutation to aspartic acid deranges electron transport

The mouse LA9 HQN-R11 cytochrome b mutant, in which the glycine residue at position 231 is replaced by aspartic acid, has increased resistance to all inhibitors of the Qn redox center. It is shown here that this single amino acid alteration has multiple and unexpectedly diverse effects upon the mitochondrial protonmotive bc1 complex. (1) The specific activities of both succinate- and ubiquinol-cytochrome c oxidoreductases in isolated mitochondria are reduced by approximately 65% in the mutant. The parallel reductions in both oxidoreductase activities are not compatible with simple Q pool kinetics for mitochondrial electron transport. (2) There is also a reduction in the relative concentration of cytochrome b in the mutant when calculated on the basis of mitochondrial protein; this decrease does not account for more than a small portion of the reduced catalytic fluxes. (3) The increased antimycin resistance of the mutant is lost upon solubilization by the detergent dodecyl maltoside of the bc1 complex from mitochondria. (4) In pre-steady-state assays of cytochrome b reduction by quinol, the mutant shows a reduced extent of reduction. It was observed in other experiments that there was less oxidant-induced extrareduction of cytochrome b in the mutant. These results could arise from a lowering of the midpoint potentials of both the cytochrome b-562 and cytochrome b-566 heme groups. Alternatively, these effects may reflect changes at the Qp and Qn quinone/quinol binding sites. (5) An unexplained observation for the mutant is the increased rate of cytochrome c1 reduction in the presence of myxothiazol. (6) These functional alterations in the LA9 HQN-R11 mutant are not accompanied by detectable changes in the spectral properties of the cytochrome b or c1 heme groups.

Studies on the CoQH2-cytochrome c reductase segment of the respiratory chain of yeast mitochondria, using mutants of the cytochrome b split gene

Our work relating to the role of cytochrome b in the CoQH2-cytochrome c reductase segment of the respiratory chain of S. cerevisiae mitochondria is reviewed here and new results are reported. The results concerning the structure-function relationship of cytochrome b in this complex, analyzed within the framework of the eight transmembrane alpha helice cytochrome b folding model, agree with the following features of the proton motive Q cycle (or SQ cycle): i) the antimycin A and myxothiazol binding domains are located on opposite sides of the inner mitochondrial membrane; and ii) the antimycin A binding domain is associated with the b562 domain, the myxothiazol domain with the b565 domain. These results were obtained from structural data derived from amino-acid sequence studies on mit- mutants and from biochemical studies of these mutants. However, functional studies are reported here that are not in agreement with the following features of the above models: i) the serial arrangement of the two hemes of cytochrome b and ii) the isolation of cytochrome b from redox changes with the couple fumarate/succinate in the presence of antimycin A and myxothiazol.