Delineating Electrogenic Reactions during Lactose/H+ Symport†

Electrogenic reactions accompanying downhill lactose/H+ symport catalyzed by the lactose permease of Escherichia coli (LacY) have been assessed using solid-supported membrane-based electrophysiology with improved time resolution. Rates of charge translocation generated by purified LacY reconstituted into proteoliposomes were analyzed over a pH range from 5.2 to 8.5, which allows characterization of two electrogenic steps in the transport mechanism: (i) a weak electrogenic reaction triggered by sugar binding and observed under conditions where H+ translocation is abolished either by acidic pH or by a Glu325 -> Ala mutation in the H+ binding site (this step with a rate constant of ~200 s-1 for wildtype LacY leads to an intermediate proposed to represent an “occluded” state) and (ii) a major electrogenic reaction corresponding to 94% of the total charge translocated at pH 8, which is pH-dependent with a maximum rate of ~30 s-1 and a pK of 7.5. This partial reaction is assigned to rate-limiting H+ release on the cytoplasmic side of LacY during turnover. These findings together with previous electrophysiological results and biochemical-biophysical studies are included in an overall kinetic mechanism that allows delineation of the electrogenic steps in the reaction pathway

Los Pirineos en el contexto de las montañas del mundo: rasgos generales y peculiaridades

29 páginas.Este trabajo introductorio intenta presentar la cordillera de los Pirineos, y especialmente sus características naturales dominantes, señalando en particular aquellas que comparte con otras cordilleras del globo, y aquellas que son peculiares de esta cadena, o compartidas con pocos sistemas montañosos similares. Veamos pues, en primer lugar, algunos rasgos generales de la mayor parte de las cordilleras.Peer reviewe

Beyond links and chains in food supply: a community OR perspective

This theoretical paper complements traditional OR approaches to improve micro-businesses’ performance. When looking at local micro-businesses, we find that current supply chain and operations theory that focuses on efficiency and economic-based criteria for chain and network integration, is inapplicable and external organisation inappropriate. An illustration shows how traditional modelling exercises may fall short in better-informing independent-minded micro-entrepreneurs on how to collaborate, even though they recognise benefits from such endeavour. The illustration concerns consideration of food micro-producers, not as links constituting a chain, but as members of a community. This paper explores two different approaches to apply Community OR research principles. On one hand, the application of OR methods to phenomena in the ‘community’; on the other, the development of research on ‘community operations’; which are symbolised as C+OR and CO+R respectively. These approaches are associated to two different research languages: of needs and for interactions. Main contributions of this paper are: first, we show that collaboration does not always need shared aims. Second, we offer a circular process where the identification of collective actions may help organisations to improve individually; and vice versa. Third, we suggest how to develop the role of a stronger collective actor by means of collaboration

Influence of phosphatidylglycerol on the uptake of liposomes by alveolar cells and on lung function

The effect of phosphatidylglycerol on the uptake of surfactant-like liposomes by alveolar type II cells and alveolar macrophages as well as the effect on endogenous surfactant function was studied in vivo. Healthy ventilated rats were intratracheally instilled with fluorescent labeled liposomes with different concentrations of phosphatidylglycerol. Lung function was determined by monitoring arterial oxygenation and, at the end of the experiment, by recording static pressure-volume curves. In addition, alveolar cells were isolated, and cell-associated fluorescence was determined using flow cytometry. The results show that, in the presence of cofactors (Ca2+, Mg 2+), phosphatidylglycerol stimulates the uptake by alveolar macrophages but hardly affects the uptake by alveolar type II cells. High concentrations of phosphatidylglycerol reduce the number of alveolar macrophages in the alveolar space and deteriorate lung function. On the other hand, the presence of cofactors protects the lung against the negative effects of phosphatidylglycerol on endogenous surfactant and alveolar macrophages. This study indicates that the phosphatidylglycerol concentration may play a fundamental role in the surfactant function and metabolism depending on the presence of so-called cofactors like calcium and magnesium; further study is needed to clarify the mechanisms involved

Distinct effects of SP-B and SP-C on the uptake of surfactant-like liposomes by alveolar cells in vivo and in vitro

The effects of surfactant protein B (SP-B) and SP-C on the uptake of surfactant-like liposomes by alveolar type II cells and alveolar macrophages were studied both in vivo and in vitro. In vivo, mechanically ventilated rats were intratracheally instilled with fluorescently labeled liposomes that had SP-B and/or SP-C incorporated in different concentrations. Consequently, the alveolar cells were isolated, and cell-associated fluorescence was determined using flow cytometry. The results show that the incorporation of SP-B does not influence the uptake, and it also does not in the presence of essential cofactors. The inclusion of SP-C in the liposomes enhanced the alveolar type II cells at a SP-C to lipid ratio of 2:100. If divalent cations (calcium and magnesium) were present at physiological concentrations in the liposome suspension, uptake of liposomes by alveolar macrophages was also enhanced. In vitro, the incorporation of SP-B affected uptake only at a protein-to-lipid ratio of 8:100, whereas the inclusion of SP-C in the liposomes leads to an increased uptake at a protein-to-lipid ratio of 1:100. From these results, it can be concluded that SP-B is unlikely to affect uptake of surfactant, whereas SP-C in combination with divalent cations and other solutes are capable of increasing the uptake