Towards biochemical fuel cells

A biochemical fuel cell is a device which converts chemical energy into electrical power. The catalysts used in this process can be either inorganic or organic type giving rise to 'inorganic fuel cells' or 'biochemical fuel cells', respectively. Biochemical fuel cells use either micro-organism or enzymes as active components to carry out electrochemical reactions. The efficiency of such a device theoretically can be as high as 90%. The difficulty in attaining these values arises due to sluggishness of electron transfer from active site to conducting electrode. This can be overcome by using mediators or by immobilizing active components on conducting electrode. We have immobilizedfad-glucose oxidase on a graphite electrode using a semiconducting chain as a bridge. At the present stage of development, such a device tacks high current densities, which is essential for commercial power generation but can be used in applications such as pacemakers and glucose sensors

Metabolism of halophilic archaea

In spite of their common hypersaline environment, halophilic archaea are surprisingly different in their nutritional demands and metabolic pathways. The metabolic diversity of halophilic archaea was investigated at the genomic level through systematic metabolic reconstruction and comparative analysis of four completely sequenced species: Halobacterium salinarum, Haloarcula marismortui, Haloquadratum walsbyi, and the haloalkaliphile Natronomonas pharaonis. The comparative study reveals different sets of enzyme genes amongst halophilic archaea, e.g. in glycerol degradation, pentose metabolism, and folate synthesis. The carefully assessed metabolic data represent a reliable resource for future system biology approaches as it also links to current experimental data on (halo)archaea from the literature

Salt dependent stability and unfolding of [Fe2-S2] ferredoxin of Halobacterium salinarum: spectroscopic investigations.

Ferredoxin from the haloarchaeon Halobacterium salinarum is a 14. 6-kDa protein with a [Fe2-S2] center and is involved in the oxidative decarboxylation of 2-oxoacids. It possesses a high molar excess of acidic amino acid residues and is stable at high salt concentration. We have purified the protein from this extreme haloarchaeon and investigated its salt-dependent stability by circular dichroism, fluorescence, and absorption techniques. The predominantly beta-sheeted protein is stable in salt concentrations of >/=1.5 M NaCl. At lower concentrations a time-dependent increase in fluorescence intensity ratio (I(360):I(330)), a decrease in the absorption at 420 nm, and a decrease in ellipticity values are observed. The rate of fluorescence intensity change at any low salt concentration is the highest, followed by absorption and ellipticity. This suggests that at low salt the unfolding of ferredoxin starts with the loss of tertiary structure, which leads to the disruption of the [Fe2-S2] center, resulting in the loss of secondary structural elements

<span style="font-size:12.0pt;font-family: "Times New Roman";mso-fareast-font-family:"Times New Roman";mso-ansi-language: EN-IN;mso-fareast-language:EN-IN;mso-bidi-language:AR-SA" lang="EN-IN">Kinetic mechanism of glucose dehydrogenase from <i>Halobacterium salinarum</i></span>

143-149<span style="font-size:12.0pt;font-family: " times="" new="" roman";mso-fareast-font-family:"times="" roman";mso-ansi-language:="" en-in;mso-fareast-language:en-in;mso-bidi-language:ar-sa"="" lang="EN-IN">The kinetic mechanism of glucose dehydrogenase (EC 1.1.1.47) from  Halobacterium salinarum was studied by initial velocity and product inhibition methods. The results suggest that both, in the forward and reverse direction, the reaction mechanism is of Bi Bi sequential ordered type involving formation of ternary complexes. NADP+ adds first and NADPH formed dissociates from the enzyme last. For the reverse direction, NADPH adds first and NADP+ leaves last. Product inhibition experiments indicate that (a), the coenzymes compete for the same site and form of the enzyme and (b), ternary abortive complexes of enzyme-NADP+-glucono-δ-lactone and enzyme-NADPH-glucose are formed. All the other inhibitions are noncompetitive.</span

An approach to biomolecular electronics and bioengineering based on coenzymes chained to solid supports

The possibility of attaching coenzymes to graphite surfaces through molecular wires in a manner such that an efficient electron transport chain is established between the bioactive molecule and the solid support has been considered. The covalent link used in these studies prevents the active molecules from diffusing away in the aqueous environment and improves their stablity and efficiency. This opens the way to employing the molecules gainfully in biomolecular electronics and bioengineering. Through the use of Molecular Orbital methods, the optimum designs for immobilisation of NAD, FAD and Cyt-c have been considered, with a view to achieving efficient electron transport. These coenzymes span the complete range of energy-transduction processes in living cells. Each of these molecules exists in two states, a reduced and an oxidised state, which can be monitored by simple spectroscopic methods. Based on the predictions of the Molecular Orbital approach, the coenzymes have been attached to graphite surfaces through polyacetylene chains. In two cases, FAD and Cyt-c, the immobilised coenzyme retained both its electrochemical and biological activity. In the case of NAD, the preparation of active surfaces with covalently attached coenzyme has so far failed. Potential applications of the chained coenzyme systems could arise in the field of biosensors, biobatteries, synthesis of value-added compounds and biomolecular electronics

Electron delocalization during the oxidation-reduction cycle of FAD and NAD: a quantum chemical approach to the design of coenzyme-immobilized bioanode for biochemical fuel cells

A biochemical fuel cell (BFC) is an electrochemical power-generating device which converts the chemical energy of a hydrogen-rich fuel (alcohol, glucose, hydrocarbons, or hydrogen itself) into electrical energy through enzyme-catalyzed oxidation-reduction reactions. The major bottleneck in the design of such systems is the slow electron transport from the substrate to the electrode. Biochemical systems that use coenzymes such as flavin adenine dinucleotide (FAD) or nicotinamide adenine dinucleotide (NAD) seem to be promising in circumventing these difficulties. We have made systematic molecular orbital calculations at the indo level on the electron flow diagrams of flavin and nicotinamide rings during their oxidation-reduction cycle. We observe from such calculations that it is possible to obtain very efficient electron transport from the coenzyme to the electrode surface by immobilizing FAD or NAD through semiconducting side chains at certain selected positions to the electrodes such as graphite. The theoretical studies have helped in the design of coenzyme-immobilized anodes which show the expected redox cycles in cyclic voltammetric studies

Metabolic profiling framework for discovery of candidate diagnostic markers of malaria

Despite immense efforts to combat malaria in tropical and sub-tropical regions, the potency of this vector-borne disease and its status as a major driver of morbidity and mortality remain undisputed. We develop an analytical pipeline for characterizing Plasmodium infection in a mouse model and identify candidate urinary biomarkers that may present alternatives to immune-based diagnostic tools. We employ (1)H nuclear magnetic resonance (NMR) profiling followed by multivariate modeling to discover diagnostic spectral regions. Identification of chemical structures is then made on the basis of statistical spectroscopy, multinuclear NMR, and entrapment of candidates by iterative liquid chromatography (LC) and mass spectrometry (MS). We identify two urinary metabolites (i) 4-amino-1-[3-hydroxy-5-(hydroxymethyl)-2,3-dihydrofuran-2-yl]pyrimidin-2(1H)-one, (ii) 2-amino-4-({[5-(4-amino-2-oxopyrimidin-1(2H)-yl)-4-hydroxy-4,5-dihydrofuran-2-yl]methyl}sulfanyl)butanoic acid that were detected only in Plasmodium berghei-infected mice. These metabolites have not been described in the mammalian or parasite metabolism to date. This analytical pipeline could be employed in prospecting for infection biomarkers in human populations