Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Multienzyme Complexes”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 991 records · Page 55Linked to original sources
PubMed1992

p56lyn catalyzes a reversible autophosphorylation reaction and a nucleoside diphosphate kinase reaction.

The reversible autophosphorylation of the pp60c-src family tyrosine kinase, p56lyn has been characterized by a simple procedure that involves the examination of the enzyme catalyzed radioisotope exchange between ATP and ADP. The equilibrium constant of the reaction was determined to be 3.31 and corresponded to a standard free energy of hydrolysis of the phosphotyrosine bond in p56lyn of -8.08 kcal/mol. GDP was capable of substituting for ADP as phosphate acceptor so that p56lyn displayed a nucleoside diphosphate kinase activity.

ATP Synthetase Complexes↗
PubMed1995

Spectroscopic identification of the axial ligands of cytochrome b560 in bovine heart succinate-ubiquinone reductase.

The axial ligands of low potential cytochrome b560 in the five subunit bovine heart succinate-ubiquinone reductase complex and in the isolated quinone binding proteins have been investigated using EPR and near-infrared magnetic circular dichroism spectroscopies. The results are consistent with bis-histidine ligation with near-perpendicular imidazole rings for cytochrome b560 in the four-subunit complex. The pronounced changes in EPR properties that accompany isolation of the cytochrome-b560 containing quinone binding proteins, are attributed to perturbation of the orientation of the imidazole rings of the heme bis-histidine ligands, rather than a change in axial ligation.

Animals↗
PubMed2005

Respiratory chain supercomplexes in plant mitochondria.

Supercomplexes are defined associations of protein complexes, which are important for several cellular functions. This "quintenary" organization level of protein structure recently was also described for the respiratory chain of plant mitochondria. Except succinate dehydrogenase (complex II), all complexes of the oxidative phosphorylation (OXPOS) system (complexes I, III, IV and V) were found to form part of supercomplexes. Compositions of these supramolecular structures were systematically investigated using digitonin solubilizations of mitochondrial fractions and two-dimensional Blue-native (BN) polyacrylamide gel electrophoresis. The most abundant supercomplex of plant mitochondria includes complexes I and III at a 1:2 ratio (I1 + III2 supercomplex). Furthermore, some supercomplexes of lower abundance could be described, which have I2 + III4, V2, III2 + IV(1-2), and I1 + III2 + IV(1-4) compositions. Supercomplexes consisting of complexes I plus III plus IV were proposed to be called "respirasome", because they autonomously can carry out respiration in the presence of ubiquinone and cytochrome c. Plant specific alternative oxidoreductases of the respiratory chain were not associated with supercomplexes under all experimental conditions tested. However, formation of supercomplexes possibly indirectly regulates alternative respiratory pathways in plant mitochondria on the basis of electron channeling. In this review, procedures to characterize the supermolecular organization of the plant respiratory chain and results concerning supercomplex structure and function are summarized and discussed.

Arabidopsis↗
PubMed1991

Inhibition of succinate-ubiquinone reductase by nitrosalicyl-N-alkylamides.

The abilities of eight nitrosalicyl-N-alkylamides to inhibit succinate-ubiquinone reductase were compared. These compounds possess both a nitro group at 3- or 5-position of the benzyl ring, and a methyl, decyl, dodecyl or tetradecyl group subsituted for the amide hydrogen of salicylamide. The result shows the following: (a) 3-Nitrosalicyl-N-alkylamides are stronger inhibitors than 5-nitrosalicyl-N-alkylamides when they have the same alkyl group. (b) The inhibitory abilities of both 3-and 5-nitrosalicyl-N-alkylamides increase with increasing alkyl group length. (c) Kinetic data show that the inhibition by 3-nitrosalicyl-N-tetradecylamide is noncompetitive with respect to the electron acceptor Q2.

Animals↗
PubMed2002

The redox state of plastoquinone pool regulates state transitions via cytochrome b6f complex in Synechocystis sp. PCC 6803.

The effects of benzoquinone analogues, phenyl-1,4-benzoquinone (PBQ) and 2,5-dibromo-3-methyl-6-isopropyl-1,4-benzoquinone (DBMIB), on state transitions in Synechocystis sp. PCC 6803 were investigated. PBQ induced a transition from state 2 to state 1 in the absence of actinic light whereas DBMIB caused a state 2 transition. 3-(3,4-Dichlorophenyl)-1,1-dimethyl urea could not eliminate the effects of PBQ and DBMIB. These results imply that the redox state of the plastoquinone pool controls the state transitions in vivo and cytochrome b6f complex is involved in this process. As a working hypothesis, we propose that the occupancy of the quinol oxidation site and the movement of the Rieske protein may be pivotal in this regulation.

Benzoquinones↗
PubMed1999

Nitric oxide mediates brain mitochondrial maturation immediately after birth.

The possible role of nitric oxide (*NO) in brain mitochondrial maturation was studied. Within the first 5 min after birth, a sharp increase in ATP concentrations was observed, coinciding with an increase in mitochondrial complex II-III (succinate-cytochrome c reductase) activity, while complex I (NADH-CoQ1 reductase) and complex IV (cytochrome c oxidase) activities remained unchanged. Under the same circumstances, cGMP concentrations were increased by 5 min after birth, correlating significantly with ATP concentrations. Since ATP concentrations also correlated significantly with mitochondrial complex II-III activity, these three parameters may be associated. Inhibition of *NO synthase activity brought about by the administration of N(omega)-nitro-L-arginine monomethyl ester to mothers prevented the postnatal increase in cGMP and ATP levels and complex II-III activity. These results suggest that early postnatal mitochondrial maturation in the brain is a *NO-mediated process.

Adenosine Triphosphate↗
PubMed2002

Cytopathies involving mitochondrial complex II.

Complex II (succinate-ubiquinone oxidoreductase) is the smallest complex in the respiratory chain and contains four nuclear-encoded subunits SdhA, SdhB, SdhC, and SdhD. It functions both as a respiratory chain component and an essential enzyme of the TCA cycle. Electrons derived from succinate can thus be directly transferred to the ubiquinone pool. Major insights into the workings of complex II have been provided by crystal structures of closely related bacterial enzymes, which have also been genetically manipulated to answer questions of structure-function not approachable using the mammalian system. This information, together with that accrued over the years on bovine complex II and by recent advances in understanding in vivo synthesis of the non-heme iron co-factors of the enzyme, is allowing better recognition of improper functioning of human complex II in diseased states. The discussion in this review is thus limited to cytopathies arising because the enzyme itself is defective or depleted by lack of iron-sulfur clusters. There is a clear dichotomy of effects. Enzyme depletion and mutations in SDHA compromise TCA activity and energy production, whereas mutations in SDHB, SDHC, and SDHD induce paraganglioma. SDHC and SDHD are the first tumor suppressor genes of mitochondrial proteins.

Animals↗
PubMed1998

Inactivation of succinate-ubiquinone reductase in substrate mixture.

Succinate-ubiquinone reductase plays an important role in the respiratory chain. Previous work showed that preparation of succinate-ubiquinone reductase was relatively stable. Though the enzyme catalysis has been extensively studied, the inactivation of succinate-ubiquinone reductase has never been reported. In the present study, the kinetic theory of the substrate reaction of irreversible inhibition described by Tsou (Adv. Enzymol. Relat. Areas Mol. Biol. 61 (1988) 381-436) was applied to study the course of an unexpected slow inactivation of succinate-ubiquinone reductase in the substrate assay mixture containing different concentrations of substrates, succinate and 2,6-dichloroindophenol. The results showed that the inactivation of succinate-ubiquinone reductase in the substrate mixture is a first order reaction. The inactivation rate decreased with increasing concentration of succinate. The values of the micro rate constants for free and succinate bound enzyme were 0.22 +/- 0.01 and 0.052 +/- 0.002 min-1, respectively. Binding with 2-thenoyl-trifluroacetone, a inhibitor specially for the quinone binding site, slowed down the inactivation. However, the rate of inactivation did not change with increasing 2,6-dichloroindophenol concentration. The study showed that succinate-ubiquinone reductase was irreversibly inactivated in the substrate mixture. The results suggest that the inactivation was not due to dilution or dissociation of the enzyme, nor to complete usage of the substrate, inhibition of the yielded product or some possible trace component in the substrate mixture, nor to modification of the essential thiol group in the succinate binding site of succinate-ubiquinone reductase. The enzyme became more stable after binding with succinate.

2,6-Dichloroindophenol↗
PubMed1982

Syntheses of biologically active ubiquinone derivatives.

Various 6-alkylubiquinone or 6-(omega-haloalkyl)ubiquinone derivatives were synthesized through a radical coupling reaction between alkanoyl or omega-haloalkanoyl peroxides and ubiquinone 0. The latter was synthesized from 2-methoxy-4-methylphenol via nitration, methylation, reduction, and oxidation by modifications of the reported methods. 6-(omega-Haloalkyl)ubiquinones were converted to 6-(omega-hydroxyalkyl)ubiquinones by a mercuric-assisted solvolysis technique. The 6-(omega-hydroxyalkyl)ubiquinones were then esterified with carboxylic acid anhydrides or carboxylic acid bearing reporting groups, such as a photoaffinity label, N-(4-azido-2-nitrophenyl)-beta-alanine, or a spin-label, 3-carboxy-2,2,5,5-tetramethyl-3-pyrrolinyl-1-oxy. The esterification was catalyzed by dicyclohexylcarbodiimide and pyridine, and the esters were purified by preparative silica gel thin-layer chromatography, developed by 3% ethanol in benzene. The spectral properties and biological functions of the synthesized ubiquinone derivatives were studied. The biological function of the synthesized compounds was followed by the ability to serve as an electron acceptor, donor, or mediator in the isolated mitochondrial electron transfer complexes of succinate-Q reductase, ubiquinol-cytochrome c reductase, and succinate-cytochrome c reductase, respectively. The concentration effect of these ubiquinone derivatives on the electron transfer reaction was compared with that of ubiquinone 10. The study of the inhibitory effect of synthesized arylazidoubiquinone on succinate-cytochrome c reductase after photolysis confirmed the existence of specific Q-binding proteins in this segment of the respiratory chain. The specific interaction between ubiquinone and protein has also gained support from the immobilization of the spin-label of a synthesized spin-labeled ubiquinone derivative.

Affinity Labels↗
PubMed1985

Effect of alkyl side chain variation on the electron-transfer activity of ubiquinone derivatives.

The effect of the alkyl side chain of the ubiquinone molecule on the electron-transfer activity of ubiquinone in mitochondrial succinate-cytochrome c reductase is studied by using synthetic ubiquinone derivatives that possess the basic ubiquinone structure of 2,3-dimethoxy-5-methyl-1,4-benzoquinone with different alkyl side chains at the 6-position. The alkyl side chains vary in chain length, degree of saturation, and location of double bonds. When a ubiquinone derivative is used as an electron acceptor for succinate-ubiquinone reductase, an alkyl side chain of six carbons is needed to obtain the maximum activity. However, when it serves as an electron donor for ubiquinol-cytochrome c reductase or as a mediator in succinate-cytochrome c reductase, an alkyl side chain of 10 carbons gives maximal efficiency. Introduction of one or two isolated double bonds into the alkyl side chain of the ubiquinone molecule has little effect on electron-transfer activity. However, a conjugated double bond system in the alkyl side chain drastically reduces electron-transfer efficiency. The effect of the conjugated double bond system on the electron-transferring efficiency of ubiquinone depends on its location in the alkyl side chain. When location is far from the benzoquinone ring, the effect is minimal. These observations together with the results obtained from photoaffinity-labeling studies lead us to conclude that flexibility in the portion of the alkyl side chain immediately adjacent to the benzoquinone ring is required for the electron-transfer activity of ubiquinone.

Alkylation↗
PubMed2000

Oxidative metabolites of 5-S-cysteinylnorepinephrine are irreversible inhibitors of mitochondrial complex I and the alpha-ketoglutarate dehydrogenase and pyruvate dehydrogenase complexes: possible implications for neurodegenerative brain disorders.

The major initial product of the oxidation of norepinephrine (NE) in the presence of L-cysteine is 5-S-cysteinylnorepinephrine which is then further easily oxidized to the dihydrobenzothiazine (DHBT) 7-(1-hydroxy-2-aminoethyl)-3,4-dihydro-5-hydroxy-2H-1, 4-benzothiazine-3-carboxylic acid (DHBT-NE-1). When incubated with intact rat brain mitochondria, DHBT-NE-1 evokes rapid inhibition of complex I respiration without affecting complex II respiration. DHBT-NE-1 also evokes time- and concentration-dependent irreversible inhibition of NADH-coenzyme Q(1) (CoQ(1)) reductase, the pyruvate dehydrogenase complex (PDHC), and alpha-ketoglutarate dehydrogenase (alpha-KGDH) when incubated with frozen and thawed rat brain mitochondria (mitochondrial membranes). The time dependence of the inhibition of NADH-CoQ(1) reductase, PDHC, and alpha-KGDH by DHBT-NE-1 appears to be related to its oxidation, catalyzed by an unknown component of the inner mitochondrial membrane, to electrophilic intermediates which bind covalently to active site cysteinyl residues of these enzyme complexes. The latter conclusion is based on the ability of glutathione to block inhibition of NADH-CoQ(1) reductase, PDHC, and alpha-KGDH by scavenging electrophilic intermediates, generated by the mitochondrial membrane-catalyzed oxidation of DHBT-NE-1, forming glutathionyl conjugates, several of which have been isolated and spectroscopically identified. The possible implications of these results to the degeneration of neuromelanin-pigmented noradrenergic neurons in the locus ceruleus in Parkinson's disease are discussed.

Animals↗
PubMed1998

Studies of the electron transport chain of the euryarcheon Halobacterium salinarum: indications for a type II NADH dehydrogenase and a complex III analog.

The components involved in the respiratory system of the euryarcheon Halobacterium salinarum were investigated by spectroscopic and polarographic techniques. Previous results about the cytochrome composition could be verified. However, under low oxygen tension, the expression of a d-type cytochrome was detected. Membranes exerted an NADH- and succinatecytochrome-c oxidoreductase as well as an NADH and succinate oxidase activity. These activities could be blocked by the following inhibitors: 7-jodocarboxylic acid, giving evidence for the presence of a type II NADH dehydrogenase, antimycin A, and myxothiazol, indicating the presence of a complex III analog, and the typical succinate dehydrogenase (SDH) and terminal oxidase inhibitors. Complex I inhibitors like rotenone and annonine were inactive, clearly excluding the presence of a coupled NADH dehydrogenase. In addition, no [Fe-S] resonances in the region of the NADH dehydrogenase (NDH) clusters could be observed after NADH addition. One of the terminal oxidases could be shown to act as a cytochrome-c oxidase with a Km value of 37 microM and an activation energy of 23.7 kJ/mol. The relative molecular mass of the endogenous c-type cytochrome could be determined as 14.1 kD. The complex III analog could be enriched after detergent extraction with Triton X-100 and hydroxylapatite (HTP) chromatography. The partially purified complex contained a Rieske iron-sulfur cluster, b- and c-type cytochromes, and was catalytically active in the decylubiquinone-cytochrome-c oxidoreductase assay.

Cytochrome d Group↗
PubMed1991

Structural and serological similarity of MHC-linked LMP and proteasome (multicatalytic proteinase) complexes.

Major histocompatibility complex (MHC) class I molecules associate with peptides derived from endogenously synthesized antigens. Cytotoxic T-lymphocytes can thus scan class I molecules and bound peptide on the surface of cells for foreign antigenic determinants. Recent evidence demonstrates that the products of trans-acting, non-class I genes in the class II region of the MHC are required in the class I antigen-processing pathway. There are genes (called HAM1 and HAM2 in the mouse) in this region that encode proteins postulated to be involved in the transport of peptide fragments into the endoplasmic reticulum for association with newly synthesized class I molecules. But, the mechanism by which such peptide fragments are produced remains a mystery. At least two genes encoding subunits of the low-molecular mass polypeptide (LMP) complex are tightly linked to the HAM1 and HAM2 genes. We show that the LMP complex is closely related to the proteasome (multicatalytic proteinase complex), an intracellular protein complex that has multiple proteolytic activities. We speculate that the LMP complex may have a role in MHC class I antigen processing, and therefore that the MHC contains a cluster of genes required for distinct functions in the antigen processing pathway.

Animals↗
PubMed1999

Revealing the structure of the oxygen-evolving core dimer of photosystem II by cryoelectron crystallography.

Here we present cryoelectron crystallographic analysis of an isolated dimeric oxygen-evolving complex of photosystem II (at a resolution of approximately 0.9 nm), revealing that the D1-D2 reaction center (RC) proteins are centrally located between the chlorophyll-binding proteins, CP43 and CP47. This conclusion supports the hypothesis that photosystems I and II have similar structural features and share a common evolutionary origin. Additional density connecting the two halves of the dimer, which was not observed in a recently described CP47-RC complex that did not include CP43, may be attributed to the small subunits that are involved in regulating secondary electron transfer, such as PsbH. These subunits are possibly also required for stabilization of the dimeric photosystem II complex. This complex, containing at least 29 transmembrane helices in its asymmetric unit, represents one of the largest membrane protein complexes studied at this resolution.

Cryoelectron Microscopy↗