Coenzyme Function Research Articles

New developments on the functions of coenzyme Q in mitochondria

The notion of a mobile pool of coenzyme Q (CoQ) in the lipid bilayer has changed with the discovery of respiratory supramolecular units, in particular the supercomplex comprising complexes I and III; in this model, the electron transfer is thought to be mediated by tunneling or microdiffusion, with a clear kinetic advantage on the transfer based on random collisions. The CoQ pool, however, has a fundamental function in establishing a dissociation equilibrium with bound quinone, besides being required for electron transfer from other dehydrogenases to complex III. The mechanism of CoQ reduction by complex I is analyzed regarding recent developments on the crystallographic structure of the enzyme, also in relation to the capacity of complex I to generate superoxide. Although the mechanism of the Q-cycle is well established for complex III, involvement of CoQ in proton translocation by complex I is still debated. Some additional roles of CoQ are also examined, such as the antioxidant effect of its reduced form and the capacity to bind the permeability transition pore and the mitochondrial uncoupling proteins. Finally, a working hypothesis is advanced on the establishment of a vicious circle of oxidative stress and supercomplex disorganization in pathological states, as in neurodegeneration and cancer.

Coenzyme Q Functionalized CdTe/ZnS Quantum Dots for Reactive Oxygen Species (ROS) Imaging

Quantum dots (QDs) have been widely used for fluorescent imaging in cells. In particular, surface functionalized QDs are of interest, since they possess the ability to recognize and detect the analytes in the surrounding nanoscale environment based on electron and hole transfer between the analytes and the QDs. Here we demonstrate that fluorescence enhancement/quenching in QDs can be switched by electrochemically modulating electron transfer between attached molecules and QDs. For this purpose, a number of redox-active coenzyme Q (CoQ) disulfide derivatives [CoQC(n)S](2) were synthesized with different alkyl chain lengths (n=1, 5, and 10). The system supremely sensitive to NADH (nicotinamide adenine dinucleotide) and superoxide radical (O(2)(.)(-)), and represents a biomimetic electron-transfer system, modeling part of the mitochondrial respiratory chain. The results of our in situ fluorescence spectroelectrochemical study demonstrate that the reduced state of [CoQC(n)S](2) significantly enhanced the fluorescence intensity of CdTe/ZnS QDs, while the oxidized state of the CoQ conjugates quench the fluorescence to varying degrees. Fluorescence imaging of cells loaded with the conjugate QD-[CoQC(n)S](2) displayed strikingly differences in the fluorescence depending on the redox state of the capping layer, thus introducing a handle for evaluating the status of the cellular redox potential status. Moreover, an MTT assay (MTT=3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) proved that the cytotoxicity of QDs was significantly reduced after immobilization by CoQ derivatives. Those unique features make CoQ derivatived QDs as a promising probe to image redox coenzyme function in vitro and in vivo.

Biotinylation, a Post-translational Modification Controlled by the Rate of Protein-Protein Association

Biotin protein ligases catalyze specific covalent linkage of the coenzyme biotin to biotin-dependent carboxylases. The reaction proceeds in two steps, including synthesis of an adenylated intermediate followed by biotin transfer to the carboxylase substrate. In this work specificity in the transfer reaction was investigated using single turnover stopped-flow and quench-flow assays. Cognate and noncognate reactions were measured using the enzymes and minimal biotin acceptor substrates from Escherichia coli, Pyrococcus horikoshii, and Homo sapiens. The kinetic analysis demonstrates that for all enzyme-substrate pairs the bimolecular rate of association of enzyme with substrate limits post-translational biotinylation. In addition, in noncognate reactions the three enzymes displayed a range of selectivities. These results highlight the importance of protein-protein binding kinetics for specific biotin addition to carboxylases and provide one mechanism for determining biotin distribution in metabolism.

Unique function of flavin coenzyme in type 2 isopentenyl diphosphate isomerase involved in archaeal isoprenoid biosynthesis

Unique function of flavin coenzyme in type 2 isopentenyl diphosphate isomerase involved in archaeal isoprenoid biosynthesis

Effects of coenzyme Q 10, α-tocopherol and ascorbic acid on oxidation of cholesterol in chicken liver pâté

The aim of this study was to determine whether supplemental addition of coenzyme Q 10 and ascorbic acid or α-tocopherol, either alone or together, can prevent oxidative damage in chicken liver pâté, as reflected by reduced formation of cholesterol oxidation products (COPs) and by preservation of sensorial quality. Separate groups of chicken liver pâtés had no supplements (control) or were supplemented with coenzyme Q 10 (0.2 g/kg) and either ascorbic acid (2 g/kg) or α-tocopherol (0.2 g/kg), or both. All products were pasteurised (82 °C) or sterilised (121 °C). Four COPs were found: 7α-, 7β-, 20α- and 25-hydroxycholesterol. The COP radical scavenger function of coenzyme Q 10 (control, 5.16 mg/kg; plus Q 10, 3.94 mg/kg) and the synchronous actions of coenzyme Q 10 and α-tocopherol (2.6 mg/kg) were confirmed in sterilised pâtés. Generally, in pasteurised and sterilised pâtés, the most efficient scavenger function was with ascorbic acid either alone or together with α-tocopherol, where the formation of COPs was below the limit of detection. An increase of 1.9 mg/kg in COP production during heating was also seen in samples without added antioxidants. There was a weak interdependence between the content of COPs and the sensory parameters of the pâté. For addition of antioxidants, in the pasteurised pâté, colour and smell were slightly improved, but flavour deteriorated; in the sterilised pâté, colour was slightly worse, with a more tender texture. Overall, instrumentally measured colour and sensory properties (except texture) showed no significant differences between pasteurisation and sterilisation.

Excited flavin and pterin coenzyme molecules in evolution

Excited flavin and pterin molecules are active in intermolecular energy transfer and in photocatalysis of redox reactions resulting in conservation of free energy. Flavin-containing pigments produced in models of the prebiotic environment are capable of converting photon energy into the energy of phosphoanhydride bonds of ATP. However, during evolution photochemical reactions involving excited FMN or FAD molecules failed to become participants of bioenergy transfer systems, but they appear in enzymes responsible for repair of UV-damaged DNA (DNA photolyases) and also in receptors of blue and UV-A light regulating vital functions of organisms. The families of these photoproteins (DNA-photolyases and cryptochromes, LOV-domain- and BLUF-domain-containing proteins) are different in the structure and in mechanisms of the photoprocesses. The excited flavin molecules are involved in photochemical processes in reaction centers of these photoproteins. In DNA photolyases and cryptochromes the excitation energy on the reaction center flavin is supplied from an antenna molecule that is bound with the same polypeptide. The role of antenna is played by MTHF or by 8-HDF in some DNA photolyases, i.e. also by molecules with known coenzyme functions in biocatalysis. Differences in the structure of chromophore-binding domains suggest an independent origin of the photoprotein families. The analysis of structure and properties of coenzyme molecules reveals some specific features that were significant in evolution for their being selected as chromophores in these proteins.

Abstract 68: Nampt regulates fatty acid synthesis, ER homeostasis, and survival in prostate cancer

Abstract Nicotinamide adenine dinucleotide (NAD) is crucial for the survival of living organisms. This coenzyme functions in both redox metabolism and as a substrate for several proteins, notably Sirtuin deacetylases and poly-(ADP ribose) polymerases, which control stress response and apoptosis in cancer. The rate limiting step of NAD biosynthesis is catalyzed by Nicotinamide phosphoribosyl transferase (Nampt). Recent evidence suggests Nampt may play a role in cancer by regulating survival. The Nampt inhibitor FK866 is in phase II clinical trials against a variety of solid malignancies, however no studies have focused on the role of NAD in prostate cancer (PCa). Because tumor cells have a high requirement for NAD and PCa has increased fatty acid synthesis, we hypothesized that Nampt is important for PCa cell survival and metabolism. Our studies demonstrate that Nampt activity is required for the survival of prostate tumor cells (PC-3, LNCaP, and DU145), but not normal prostate epithelial cells, as determined by treatment with FK866. Exogenous NAD rescued cell death, indicating FK866 is a specific inhibitor of Nampt. To test whether PCa cells can rely on de novo NAD synthesis, we treated cell lines with FK866 and added back nicotinic acid, the substrate for the de novo pathway. Only DU145 cell survival was rescued by nicotinic acid demonstrating that NAD biosynthesis pathways are heterogeneous in PCa. Furthermore, expression of Nicotinic acid phosphoribosyl transferase (Naprt1), the rate-limiting step of the de novo pathway, correlated with the rescue by nicotinic acid in DU145 cells. Additionally, Nampt inhibition activated endoplasmic reticulum (ER) stress and autophagy in a pro-survival manner in all cell lines. Interestingly, FK866 also dramatically reduced fatty acid synthesis in PC-3 and DU145 cells, independent of fatty acid synthase levels. However, LNCaP cells showed no decrease in 14C-acetate incorporation. Robust phosphorylation of ACC occured in DU145 and PC-3 cells upon treatment with FK866, and this effect was rescued by adding back NAD. This correlated with reduced ATP levels and activation (phosphorylation) of AMPK at T172. LNCaP cells had a less dramatic depletion of ATP and no changes in AMPK or ACC phosphorylation, indicating a potential mechanism of fatty acid synthesis shutdown. However, lipid synthesis (as measured by incorporation of 14C-choline) was reduced in all 3 cell lines, albeit to a lesser extent in LNCaP cells. Overall, these findings demonstrate a novel role for Nampt in PCa, and highlight the contribution of NAD to ER homeostasis, fatty acid synthesis, and survival. Targeting NAD biosynthesis could be a novel approach to disrupting PCa cell survival and lipid synthesis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 68.

Structure and Mechanism of the glmS Ribozyme

The self-cleaving glmS ribozyme is a mechanistically unique functional RNA among both riboswitches and RNA catalysts as its catalytic activity provides the basis of genetic regulation and depends upon glucosamine-6-phosphate (GlcN6P) as a coenzyme. A substantial body of biochemical and biophysical data relating the structure and function of the glmS ribozyme has been amassed, in our laboratory and others, in a relatively short period of time since its discovery. However, a precise and comprehensive mechanistic understanding of coenzyme function in glmS ribozyme self-cleavage has not been elaborated. Careful consideration of the available biochemical and biophysical data relating the structure and function of the glmS ribozyme necessitates that general acid and general base catalysis in a coenzyme-dependent active site mechanism of RNA cleavage are inherently interdependent. We propose a comprehensive mechanistic model wherein the coenzyme, GlcN6P, functions both as the initial general base catalyst and consequent general acid catalyst within a proton-relay thus fulfilling the apparent biochemical requirements for activity. This analysis in combination with other considerations regarding the effects of coenzyme binding on riboswitch structure and function suggests that the development of glmS ribozyme agonists as prospective antibiotic compounds must satisfy strict chemical requirements for binding and activity.

How I became a biochemist

How I became a biochemist

Functions of coenzyme Q10 in inflammation and gene expression

Clinical studies demonstrated the efficacy of Coenzyme Q10 (CoQ10) as an adjuvant therapeutic in cardiovascular diseases, mitochondrial myopathies and neurodegenerative diseases. More recently, expression profiling revealed that Coenzyme Q10 (CoQ10) influences the expression of several hundred genes. To unravel the functional connections of these genes, we performed a text mining approach using the Genomatix BiblioSphere. We identified signalling pathways of G-protein coupled receptors, JAK/STAT, and Integrin which contain a number of CoQ10 sensitive genes. Further analysis suggested that IL5, thrombin, vitronectin, vitronectin receptor, and C-reactive protein are regulated by CoQ10 via the transcription factor NFkappaB1. To test this hypothesis, we studied the effect of CoQ10 on the NFkappaB1-dependent pro-inflammatory cytokine TNF-alpha. As a model, we utilized the murine macrophage cell lines RAW264.7 transfected with human apolipoprotein E3 (apoE3, control) or pro-inflammatory apoE4. In the presence of 2.5 microM or 75 microM CoQ10 the LPS-induced TNF-alpha response was significantly reduced to 73.3 +/- 2.8% and 74.7 +/- 8.9% in apoE3 or apoE4 cells, respectively. Therefore, the in silico analysis as well as the cell culture experiments suggested that CoQ10 exerts anti-inflammatory properties via NFkappaB1-dependent gene expression.

Acyl derivatives of coenzyme A inhibit platelet function via antagonism at P2Y1 and P2Y12 receptors: A new finding that may influence the design of anti-thrombotic agents

We have performed a detailed investigation of the effects on platelet function of coenzyme A (CoA) and several acyl-CoAs. Platelet aggregation was measured by turbidimetry and by platelet counting; platelet shape change was measured using light scattering; P-selectin, Ca2+ mobilization and vasodilator-stimulated phosphoprotein (VASP) phosphorylation were measured by flow cytometry. The compounds investigated inhibited ADP-induced platelet aggregation; those with saturated acyl groups containing 16-18 carbons were most effective. The effects of palmitoyl-CoA (16:0) were studied in depth. It inhibited platelet shape change and Ca2+ mobilization brought about by ADP (but not other agonists) indicating antagonism at P2Y1 receptors, and also inhibited ADP-induced P-selectin expression. Effects of palmitoyl-CoA on the platelet aggregation and Ca2+ mobilization induced by several different agonists and agonist combinations were compared with those of MRS 2179 (a P2Y1 antagonist) and AR-C69931 (a P2Y12 antagonist), and were consistent with palmitoyl-CoA acting mainly at P2Y1 but also with partial antagonism at P2Y12 receptors. Antagonism at P2Y12 receptors was confirmed in studies of VASP-phosphorylation. Palmitoyl-CoA did not act as an antagonist at P2X1 receptors. The results are discussed in relation to the possibility that acyl-CoAs may contribute as endogenous modulators of platelet function and might serve as lead compounds for the design of novel antithrombotics.

Essential Role of an Active-Site Guanine in glmS Ribozyme Catalysis

The glmS ribozyme is a catalytic riboswitch that is activated for endonucleolytic cleavage by the coenzyme glucosamine-6-phosphate. Using kinetic assays and X-ray crystallography, we identify an active-site mutation of a conserved guanine that abolishes catalysis without perturbing coenzyme binding. Our results provide evidence that coenzyme function requires a specific nucleobase to interact with the nucleophile of the cleavage reaction.

New insights into the pathophysiology of cobalamin deficiency

Cobalamin-deficient (Cbl-D) central neuropathy in the rat is associated with a locally increased expression of neurotoxic tumour necrosis factor-alpha (TNF-alpha) and a locally decreased expression of neurotrophic epidermal growth factor (EGF). These recent findings suggest that cobalamin oppositely regulates the expression of TNF-alpha and EGF, and raise the possibility that these effects might be independent of its coenzyme function. Furthermore, adult Cbl-D patients have high levels of TNF-alpha and low levels of EGF in the serum and cerebrospinal fluid. Serum levels of TNF-alpha and EGF of cobalamin-treated patients normalize concomitantly with haematological disease remission. These observations suggest that cobalamin deficiency induces an imbalance in TNF-alpha and EGF levels in biological fluids that might have a role in the pathogenesis of the damage caused by pernicious anaemia.

Effect of atorvastatin on left ventricular diastolic function and ability of coenzyme Q 10 to reverse that dysfunction

This study evaluated left ventricular diastolic function with Doppler echocardiography before and after statin therapy. Statin therapy worsened diastolic parameters in most patients; coenzyme Q(10) supplementation in patients with worsening diastolic function with statin therapy improved parameters of diastolic function.

Cellular redox poise modulation; the role of coenzyme Q 10, gene and metabolic regulation

In this communication, the concept is developed that coenzyme Q 10 has a toti-potent role in the regulation of cellular metabolism. The redox function of coenzyme Q 10 leads to a number of outcomes with major impacts on sub-cellular metabolism and gene regulation. Coenzyme Q 10's regulatory activities are achieved in part, through the agency of its localization in the various sub-cellular membrane compartments. Its fluctuating redox poise within these membranes reflects the cell's metabolic micro-environments. As an integral part of this process, H 2O 2 is generated as a product of the normal electron transport systems to function as a mitogenic second messenger informing the nuclear and mitochondrial (chloroplast) genomes on a real-time basis of the status of the sub-cellular metabolic micro-environments and the needs of that cell. Coenzyme Q 10 plays a major role both in energy conservation, and energy dissipation as a component of the uncoupler protein family. Coenzyme Q 10 is both an anti-oxidant and a pro-oxidant and of the two the latter is proposed as its more important cellular function. Coenzyme Q 10 has been reported, to be of therapeutic benefit in the treatment of a wide range of age related degenerative systemic diseases and mitochondrial disease. Our over-arching hypotheses on the central role played by coenzyme Q 10 in redox poise changes, the generation of H 2O 2, consequent gene regulation and metabolic flux control may account for the wide ranging therapeutic benefits attributed to coenzyme Q 10.

Synthetic chemistry and chemical precedents for understanding the structure and function of acetyl coenzyme A synthase.

Acetyl coenzyme A synthase (ACS), found in acetogenic and methanogenic organisms, is responsible for the synthesis and breakdown of acetate. The mechanism by which methylcob(III)alamin, CO and coenzyme A are assembled/disassembled at the active-site A-cluster involves a number of biologically unprecedented intermediates. In the past two years, two protein crystal structures have significantly enhanced the understanding of the structure of the active-site A-cluster, responsible for catalysis. The structure reports spawned a number of important questions regarding the metal ion constitution of the active enzyme, the structure(s) of the spectroscopically identified states and the details of the catalytic mechanism. This Commentary addresses these issues in the framework of existing synthetic and chemical precedent studies aimed at developing rational structure-function correlations and presents structural and reactivity targets for future studies.

Metabolism and function of coenzyme Q

Coenzyme Q (CoQ) is present in all cells and membranes and in addition to be a member of the mitochondrial respiratory chain it has also several other functions of great importance for the cellular metabolism. This review summarizes the findings available to day concerning CoQ distribution, biosynthesis, regulatory modifications and its participation in cellular metabolism. There are a number of indications that this lipid is not always functioning by its direct presence at the site of action but also using e.g. receptor expression modifications, signal transduction mechanisms and action through its metabolites. The biosynthesis of CoQ is studied in great detail in bacteria and yeast but only to a limited extent in animal tissues and therefore the informations available is restricted. However, it is known that the CoQ is compartmentalized in the cell with multiple sites of biosynthesis, breakdown and regulation which is the basis of functional specialization. Some regulatory mechanisms concerning amount and biosynthesis are established and nuclear transcription factors are partly identified in this process. Using appropriate ligands of nuclear receptors the biosynthetic rate can be increased in experimental system which raises the possibility of drug-induced upregulation of the lipid in deficiency. During aging and pathophysiological conditions the tissue concentration of CoQ is modified which influences cellular functions. In this case the extent of disturbances is dependent on the localizaion and the modified distribution of the lipid at cellular and membrane levels.

Functions of the D-ribosyl moiety and the lower axial ligand of the nucleotide loop of coenzyme B(12) in diol dehydratase and ethanolamine ammonia-lyase reactions.

The roles of the D-ribosyl moiety and the bulky axial ligand of the nucleotide loop of adenosylcobalamin in coenzymic function have been investigated using two series of coenzyme analogs bearing various artificial bases. The 2-methylbenzimidazolyl trimethylene analog that exists exclusively in the base-off form was a totally inactive coenzyme for diol dehydratase and served as a competitive inhibitor. The benzimidazolyl trimethylene analog and the benzimidazolylcobamide coenzyme were highly active for diol dehydratase and ethanolamine ammonia-lyase. The imidazolylcobamide coenzyme was 59 and 9% as active as the normal coenzyme for diol dehydratase and ethanolamine ammonia-lyase, respectively. The latter analog served as an effective suicide coenzyme for both enzymes, although the partition ratio (k(cat)/k(inact)) of 630 for ethanolamine ammonia-lyase is much lower than that for diol dehydratase. Suicide inactivation was accompanied by the accumulation of a cob(II)amide species, indicating irreversible cleavage of the coenzyme Co-C bond during the inactivation. It was thus concluded that the bulkiness of a Co-coordinating base of the nucleotide loop is essential for both the initial activity and continuous catalytic turnovers. Since the k(cat)/k(inact) value for the imidazolylcobamide in diol dehydratase was 27-times higher than that for the imidazolyl trimethylene analog, it is clear that the ribosyl moiety protects the reaction intermediates from suicide inactivation. Stopped-flow measurements indicated that the rate of Co-C bond homolysis is essentially unaffected by the bulkiness of the Co-coordinating base for diol dehydratase. Thus, it seems unlikely that the Co-C bond is labilized through a ground state mechanochemical triggering mechanism in diol dehydratase.

Biochemistry during the Life and Times of Hans Krebs and Fritz Lipmann

Biochemistry during the Life and Times of Hans Krebs and Fritz Lipmann

Kinetic and spectral investigation of allosteric interaction of coenzymes with 2-oxo acid dehydrogenase complexes

The possible role of thiamine pyrophosphate (TPP) in the regulation of both multienzyme pyruvate dehydrogenase complex (PDC) and 2-oxoglutarate dehydrogenase complex (OGDC) has been investigated by kinetic and spectral methods. The purified PDC and OGDC from animal heart muscle were near saturated with endogenous TPP. The PDC containing the bound coenzyme showed hysteretic behaviour manifested in a lag phase of the catalysed reaction after the contact of PDC with substrates. Exogenous TPP added to the full reaction medium led to a disappearance of the lag phase and to strong reduction of the Michaelis constant ( K m) value for pyruvate, and more moderate decrease of K m for both coenzyme A and NAD. In the case of OGDC exogenous TPP also decreased S 0.5 ( K m) for substrate 2-oxoglutarate. In addition, exogenous TPP changed both the UV and circular dichroism spectra of PDC and last one of OGDC, and lowered the fluorescence emission of the multienzyme complexes containing bound molecules of endogenous coenzyme in their active sites. Thiamine pyrophosphate seems to play, besides its coenzyme function, the role of positive allosteric effector which causes conformational changes of the multienzyme complexes and increases their affinity to substrates.