Trapping the transition state of an ATP-binding cassette transporter: Evidence for a concerted mechanism of maltose transport

High-affinity uptake into bacterial cells is mediated by a large class of periplasmic binding protein-dependent transport systems, members of the ATP-binding cassette superfamily. In the maltose transport system of Escherichia coli, the periplasmic maltose-binding protein binds its substrate maltose with high affinity and, in addition, stimulates the ATPase activity of the membrane-associated transporter when maltose is present. Vanadate inhibits maltose transport by trapping ADP in one of the two nucleotide-binding sites of the membrane transporter immediately after ATP hydrolysis, consistent with its ability to mimic the transition state of the γ-phosphate of ATP during hydrolysis. Here we report that the maltose-binding protein becomes tightly associated with the membrane transporter in the presence of vanadate and simultaneously loses its high affinity for maltose. These results suggest a general model explaining how ATP hydrolysis is coupled to substrate transport in which a binding protein stimulates the ATPase activity of its cognate transporter by stabilizing the transition state.

VanX, a bacterial d-alanyl-d-alanine dipeptidase: Resistance, immunity, or survival function?

The zinc-containing d-alanyl-d-alanine (d-Ala-d-Ala) dipeptidase VanX has been detected in both Gram-positive and Gram-negative bacteria, where it appears to have adapted to at least three distinct physiological roles. In pathogenic vancomycin-resistant enterococci, vanX is part of a five-gene cluster that is switched on to reprogram cell-wall biosynthesis to produce peptidoglycan chain precursors terminating in d-alanyl-d-lactate (d-Ala-d-lactate) rather than d-Ala-d-Ala. The modified peptidoglycan exhibits a 1,000-fold decrease in affinity for vancomycin, accounting for the observed phenotypic resistance. In the glycopeptide antibiotic producers Streptomyces toyocaensis and Amylocatopsis orientalis, a vanHAX operon may have coevolved with antibiotic biosynthesis genes to provide immunity by reprogramming cell-wall termini to d-Ala-d-lactate as antibiotic biosynthesis is initiated. In the Gram-negative bacterium Escherichia coli, which is never challenged by the glycopeptide antibiotics because they cannot penetrate the outer membrane permeability barrier, the vanX homologue (ddpX) is cotranscribed with a putative dipeptide transport system (ddpABCDF) in stationary phase by the transcription factor RpoS (σs). The combined action of DdpX and the permease would permit hydrolysis of d-Ala-d-Ala transported back into the cytoplasm from the periplasm as cell-wall crosslinks are refashioned. The d-Ala product could then be oxidized as an energy source for cell survival under starvation conditions.

The Role of Iron-Deficiency Stress Responses in Stimulating Heavy-Metal Transport in Plants1

Plant accumulation of Fe and other metals can be enhanced under Fe deficiency. We investigated the influence of Fe status on heavy-metal and divalent-cation uptake in roots of pea (Pisum sativum L. cv Sparkle) seedlings using Cd2+ uptake as a model system. Radiotracer techniques were used to quantify unidirectional 109Cd influx into roots of Fe-deficient and Fe-sufficient pea seedlings. The concentration-dependent kinetics for 109Cd influx were graphically complex and nonsaturating but could be resolved into a linear component and a saturable component exhibiting Michaelis-Menten kinetics. We demonstrated that the linear component was apoplastically bound Cd2+ remaining in the root cell wall after desorption, whereas the saturable component was transporter-mediated Cd2+ influx across the root-cell plasma membrane. The Cd2+ transport system in roots of both Fe-deficient and Fe-sufficient seedlings exhibited similar Michaelis constant values, 1.5 and 0.6 μm, respectively, for saturable Cd2+ influx, whereas the maximum initial velocity for Cd2+ uptake in Fe-deficient seedlings was nearly 7-fold higher than that in Fe-grown seedlings. Investigations into the mechanistic basis for this response demonstrated that Fe-deficiency-induced stimulation of the plasma membrane H+-ATPase did not play a role in the enhanced Cd2+ uptake. Expression studies with the Fe2+ transporter cloned from Arabidopsis, IRT1, indicated that Fe deficiency induced the expression of this transporter, which might facilitate the transport of heavy-metal divalent cations such as Cd2+ and Zn2+, in addition to Fe2+.

Modelagem e análise das cadeias de suprimentos globais e resilientes baseadas em rede de Petri.

Em um cenário de aumento de competitividade, crescente expectativa por inovações do produto e necessidade de atender diferentes perfis de consumidores, o conceito de gerenciamento de cadeias de suprimentos globais (GSCM) surge como uma estratégia para coordenar mais eficazmente as atividades dispersas geograficamente dos sistemas produtivos. Na adoção do GSCM, as organizações devem lidar com rupturas que impactam no gerenciamento das suas atividades, tais como a interrupção de vias de transporte, pane no fornecimento de energia, desastres naturais e até ataques terroristas. Nesse contexto, o trabalho introduz um procedimento sistematizado para modelagem das cadeias de suprimentos visto como um sistema a eventos discretos e sua análise por simulação das atividades do GSCM baseada em técnicas formais como a rede de Petri (PN) e o Production Flow Schema (PFS). Um exemplo é também apresentado para ilustrar e comprovar as vantagens do método proposto na análise do GSCM.

PCDD/F Emissions from Light-Duty Diesel Vehicles Operated under Highway Conditions and a Diesel-Engine Based Power Generator

PCDD/F emissions from three light-duty diesel vehicles–two vans and a passenger car–have been measured in on-road conditions. We propose a new methodology for small vehicles: a sample of exhaust gas is collected by means of equipment based on United States Environmental Protection Agency (U.S. EPA) method 23A for stationary stack emissions. The concentrations of O2, CO, CO2, NO, NO2 and SO2 have also been measured. Six tests were carried out at 90-100 km/h on a route 100 km long. Two additional tests were done during the first 10 minutes and the following 60 minutes of the run to assess the effect of the engine temperature on PCDD/F emissions. The emission factors obtained for the vans varied from 1800 to 8400 pg I-TEQ/Nm3 for a 2004 model year van and 490-580 pg I-TEQ/Nm3 for a 2006 model year van. Regarding the passenger car, one run was done in the presence of a catalyst and another without, obtaining emission factors (330-880 pg I-TEQ/Nm3) comparable to those of the modern van. Two other tests were carried out on a power generator leading to emission factors ranging from 31 to 78 pg I-TEQ/Nm3. All the results are discussed and compared with literature.

Prospects for Energy Supply and Demand in the Southern Mediterranean: Scenarios for 2010-30. MEDPRO Technical Report No. 22/December 2012

The aim of this technical report is to quantify alternative energy demand and supply scenarios for ten southern and eastern Mediterranean countries up to 2030. The report presents the model-based results of four alternative scenarios that are broadly in line with the MEDPRO scenario specifications on regional integration and cooperation with the EU. The report analyses the main implications of the scenarios in the following areas: • final energy demand by sector (industry, households, services, agriculture and transport); • the evolution of the power generation mix, the development of renewable energy sources and electricity exports to the EU; • primary energy production and the balance of trade for hydrocarbons; • energy-related CO2 emissions; and • power generation costs.

Predicting effects of an electric generating station on wetland passerine birds : Wisconsin power plant impact study /

Grant R803971.

Report to the Congress on energy conservation potential of off-highway recreational motor vehicles.

Mode of access: Internet.

Electric and hybrid vehicle demonstration. 1978.

Mode of access: Internet.

Feasibility demonstration of a novel, flat-belt, continuously variable transmission for automotive and electric-hybrid vehicle application. Final report.

Energy Department, Washington, D.C.

AC powertrain for an electric vehicle - phase 2 and phase 3. Final report.

Energy Department, Office of Vehicle and Engine Research and Development, Washington, D.C.

The SPM energy flux method for predicting longshore transport rate /

"June 1980."

Energy demand forecasting [microform] : hearings before the Subcommittee on Investigations and Oversight of the Committee on Science and Technology, U.S. House of Representatives, Ninety-seventh Congress, first session, June 1, 2, 1981.

"No. 14."

Uptake and metabolism of ginsenoside Rh2 and its aglycon protopanaxadiol by Caco-2 cells

The uptake and metabolism profiles of ginsenoside Rh2 and its aglycon protopanaxadiol (ppd) were studied in the human epithelial Caco-2 cell line. High-performance liquid chromatography-mass spectrometry was applied to determine Rh2 and its aglycon ppd concentration in the cells at different pH, temperature, concentration levels and in the presence or absence of inhibitors. Rh2 uptake was time and concentration dependent, and its uptake rates were reduced by metabolic inhibitors and influenced by low temperature, thus indicating that the absorption process was energy-dependent. Drug uptake was maximal when the extracellular pH was 7.0 for Rh2 and 8.0 for ppd. Rh2 kinetic analysis showed that a non-saturable component (K-d 0.17 nmol (.) h(-1) (.) mg(-1) protein) and an active transport system with a K-m of 3.95 mumol (.) l(-1) and a V-max of 4.78 nmol(.)h(-1) (.)mg(-1) protein were responsible for the drug uptake. Kinetic analysis of ppd showed a non-saturable component (K-d 0.78 nmol (.) h(-1) (.) mg(-1) protein). It was suggested that active extrusion of P-glycoprotein and drug degradation in the intestine may influence Rh2 bioavailability.

Eliminating non-renewable CO2 emissions from sewage treatment: An anaerobic migrating bed reactor pilot plant study

The aim of this work was to demonstrate at pilot scale a high level of energy recovery from sewage utilising a primary Anaerobic Migrating Bed Reactor (AMBR) operating at ambient temperature to convert COD to methane. The focus is the reduction in non-renewable CO2 emissions resulting from reduced energy requirements for sewage treatment. A pilot AMBR was operated on screened sewage over the period June 2003 to September 2004. The study was divided into two experimental phases. In Phase 1 the process operated at a feed rate of 10 L/h (HRT 50 h), SRT 63 days, average temperature 28 degrees C and mixing time fraction 0.05. In Phase 2 the operating parameters were 20 L/h, 26 days, 16 degrees C and 0.025. Methane production was 66% of total sewage COD in Phase 1 and 23% in Phase 2. Gas mixing of the reactor provided micro-aeration which suppressed sulphide production. Intermittent gas mixing at a useful power input of 6 W/m(3) provided satisfactory process performance in both phases. Energy consumption for mixing was about 1.5% of the energy conversion to methane in both operating phases. Comparative analysis with previously published data confirmed that methane supersaturation resulted in significant losses of methane in the effluent of anaerobic treatment systems. No cases have been reported where methane was considered to be supersaturated in the effluent. We have shown that methane supersaturation is likely to be significant and that methane losses in the effluent are likely to have been greater than previously predicted. Dissolved methane concentrations were measured at up to 2.2 times the saturation concentration relative to the mixing gas composition. However, this study has also demonstrated that despite methane supersaturation occurring, microaeration can result in significantly lower losses of methane in the effluent (< 11% in this study), and has demonstrated that anaerobic sewage treatment can genuinely provide energy recovery. The goal of demonstrating a high level of energy recovery in an ambient anaerobic bioreactor was achieved. An AMBR operating at ambient temperature can achieve up to 70% conversion of sewage COD to methane, depending on SRT and temperature. (c) 2006 Wiley Periodicals, Inc.