The relative positions of the centers of mass of the 21 proteins of the 30S ribosomal subunit from Escherichia coli have been determined by triangulation using neutron scattering data. The resulting map of the quaternary structure of the small ribosomal subunit is presented, and comparisons are made with structural data from other sources.

An electricity-generating bacterium, Geobacter sulfurreducens PCA, was inoculated into a single-chamber, air-cathode microbial fuel cell (MFC) in order to determine the maximum electron transfer rate from bacteria to the anode. To create anodic reaction-limiting conditions, where electron transfer from bacteria to the anode is the rate-limiting step, anodes with electrogenic biofilms were reduced in size and tests were conducted using anodes of six different sizes. The smallest anode (7 cm 2 , or 1.5 times larger than the cathode) achieved an anodic reaction-limiting condition as a result of a limited mass of bacteria on the electrode. Under these conditions, the limiting current density reached a maximum of 1,530 mA/m 2 , and power density reached a maximum of 461 mW/m 2 . Per-biomass efficiency of the electron transfer rate was constant at 32 fmol cell ؊1 day ؊1 (178 mol g of protein ؊1 min ؊1 ), a rate comparable to that with solid iron as the electron acceptor but lower than rates achieved with fumarate or soluble iron. In comparison, an enriched electricity-generating consortium reached 374 mol g of protein ؊1 min ؊1 under the same conditions, suggesting that the consortium had a much greater capacity for electrode reduction. These results demonstrate that per-biomass electrode reduction rates (calculated by current density and biomass density on the anode) can be used to help make better comparisons of electrogenic activity in MFCs.Microbial fuel cells (MFCs) are devices that exploit microorganisms as "biocatalysts" of generating electric power from organic matter. MFC systems are being researched as a method of recovering energy from waste as electrical power (10,23,24,35) and generating power from aquatic sediments on the bottom of the ocean (25, 42) or from rice paddy soil (13,14). Recent technical improvements of MFC system architecture have increased power densities from Ͻ0.1 mW/m 2 to Ͼ2,400 mW/m 2 (normalized by the anode surface area) during the past several years in systems lacking exogenous electron shuttles (22,24). However, continued improvements are still needed for improved power densities, reduced costs for materials, and the development of large-scale devices (8).The two common ways of expressing MFC performance for power generation are power normalized to the projected surface area of an electrode (power density; mW/m 2 ) and power per unit of reactor volume (power output; W/m 3 ) (35). Many studies of MFCs have used power density based on the assumption that the biocatalytic activity of the anode limits power production (16,24,35,39). However, variations in the reactor volume (2, 38), composition of the proton-exchange membrane (17), catholyte reactions (32, 34), substrates (21), and anode materials (5, 33) often make it difficult to know which factors actually limit power production. There are various potential losses that can limit power output, such as microbial electron transfer to the anode, solution resistance, membrane resistance, and reduction reaction on the cathode (16, 35). The...

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An electro-conductive enzyme membrane has been synthesized at a platinum electrode surface by electrochemical polymerization of pyrrole in the presence of glucose oxidase, while retaining enzyme activity and reversible electron transfer between the enzyme molecules and the electrode.Electrochemical synthesis of conductive polymer membranes has gained an increasing interest as it is a simple process with many applications. Electropolymerized electrodes of polymer batteries have been extensively studied along with electrochromic displays. 1 4 Murray and his co-workers reported an ion-gate membrane which is made of electrochemically synthesized polypyrrole and is electrochemically controllable by ion permeability.5 Electrochemical control of amino acid permeability has also been performed with an electrochemically synthesized polypyrrole membrane .6 Shinohara et al. have assembled an artificial synapse using an electrochemically synthesized polypyrrole membrane, which electrically released neurotransmitter molecules in the cell.7.8A technique, for the entrapment of an enzyme in a conductive polymer, was p r o p ~s e d . ~ However, the technique had difficulty with the electroconductivity of the enzymeentrapped polymer and electron transfer between the enzyme and polymer matrix. A novel membrane, electro-conductive enzyme membrane, has been prepared by electrochemical polymerization of pyrrole in the presence of glucose oxidase. Electron transfer has been shown between glucose oxidase and polypyrrole matrix in the membrane.Electrochemical polymerization was carried out in a glass vessel equipped with a platinum wire electrode (0.5 mm in diameter, 7.5 mm in length), a platinum plate electrode (10 x 5 mm2), and a Ag/AgCl reference electrode. These electrodes were connected to a potentiostat (Hokuto Denko, Model HA-301) and a coulometer (Hokuto Denko, Model HF-201). Pyrrole was dissolved in 0.1 mol dm-3 KCl solution to make a 0.1 mol dm-3 solution which was deoxygenated before use. Glucose oxidase (GOD)(TOYOBO Co., grade 11, 113 U mg-1) was added to 1 cm3 of the solution, which was transferred to the glass vessel. The electrode potential of the platinum wire electrode was set at 0.7 V vs. Ag/AgCl to initiate electrochemical polymerization, this was held at a fixed charge. A black membrane deposited on the electrode surface. The membranes were synthesized at various concentrations of GOD and at different charges, and were thoroughly washed with 0.1 mol dm-3 KCl solution.The polypyrrole/GOD membrane was assayed for enzyme activity and characterized by electrochemical measurements. The membrane was immersed in a 0.1 mol dm-3 citrate buffer solution (pH 5.5) containing 0.17 mmol dm-3 3,3'-dimethoxy benzidine, 93 mmol dm-3 glucose, and 7 mU cm-3 peroxidase (TOYOBO Co., grade 111, 127 U mg--1).10 The solution was incubated at 25°C and stirred. An aliquot was assayed for absorbance at 436 nm with a spectrophotometer (Japan Spectroscopic Co., Model UVIDEC-610C).Each membrane, synthesized under different conditions, showed enz...

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The immobilization of biomolecules is an important technique for bio-analysis, and can be applied to biosensors with both high selectivity and high sensitivity. Many researchers have developed immobilization techniques to optimize these characteristics. In the last two decades, an immobilization technique that meets the desired requirements was developed by using polyelectrolytes to form complexes, based on the electrostatic binding between polycations and polyanions. This review summarizes the techniques used for the immobilization of biomolecules by polyelectrolyte complexes; it also discusses related subjects.