Many of the interesting physics processes to be measured at the LHC have a signature involving one or more isolated electrons. The electron reconstruction and identification efficiencies of the ATLAS detector at the LHC have been evaluated using proton-proton collision data collected in 2011 at sqrt(s) = 7 TeV and corresponding to an integrated luminosity of 4.7/fb. Tag-and-probe methods using events with leptonic decays of W and Z bosons and J/psi mesons are employed to benchmark these performance parameters. The combination of all measurements results in identification efficiencies determined with an accuracy at the few per mil level for electron transverse energy greater than 30 GeV.
of perspectives. An evolutionary approach can be used to understand what conditions favor the expression of aggressive behavior. The aim of a mechanistic analysis is to understand the genetic and biochemical basis of aggression. Finally, since aggression is often viewed as disruptive to human society, techniques for predicting and influencing the aggressive potential of both normal and pathologically aggressive individuals are of obvious practical value. In general, the first volume is edited well and there are a number of recent references. The introductory chapter usefully abstracts the main points of the following twelve chapters, and all articles are accessible to the nonspecialist. Because of the extreme breadth of the material covered, it is impossible for a single reviewer to critique knowledgeably all the chapters, which range from studies of chimpanzee behavior to the role of therapy in resolving conflicts between family members. Medically oriented readers should be aware, however, that the evolutionary perspective is seriously shortchanged. Barchas's claim that the evolutionist cannot reliably predict the conditions most likely to elicit aggression is simply false; there is an extensive theoretical literature on this subject whose predictions are confirmed by numerous empirical studies. The broad usefulness of such an approach is all too obvious when one reads the review of biochemical, pharmacological, and genetic studies of aggression. Any animal behaviorist would have predicted the relatively recent physiological findings that "predatory aggression" (i.e., the capture of food) is distinct from other types of aggression involving the defense of resources or offspring. The many theoretical and field studies of parent-offspring conflict and changes in behavior associated with the onset of sexual maturity would be relevant to the two chapters on adolescent aggressive behavior. A comparative anthropological review of aggression in "primitive" societies would also have helped to place our own aggressive tendencies in better perspective. The references found in articles published in the journal Aggressive Behavior from 1975-1979, which comprise the second volume, can be used to gain entry into a variety of areas which deal with aggression. Although once again some fields are under-represented, the fine subject index can be used to locate articles whose bibliographies will lead into subjects poorly covered by this journal. This saves the reader from having to consult directly the twenty volumes, although the price for this service is rather high.
Liposomes that destabilize at mildly acidic pH are efficient tools for delivering water-soluble drugs into the cell cytoplasm. However, their use in vivo is limited because of their rapid uptake from circulation by the reticuloendothelial system. Lipid-anchored polyethylene glycol (PEG-PE) prolongs the circulation time of liposomes by steric stabilization. We have found that addition of PEG-PE to the membrane of pH-sensitive liposomes composed of cholesteryl hemisuccinate (CHEMS) and dioleoylphosphatidylethanolamine (DOPE) confers steric stability to these vesicles. This modification significantly decreases the pH-dependent release of a charged water-soluble fluorophore, calcein, from liposomes suspended in buffer or cell culture medium. However, the ability of such liposomes to release calcein intracellularly, measured by a novel flow cytometry technique involving dual fluorescence labeling, remains unaltered. As expected, the release of calcein from liposomes endocytosed by cells is inhibited upon pretreatment of the cells with NH4Cl, an inhibitor of endosome acidification. The unique properties of these liposomes were also demonstrated in vivo. The distribution kinetics of 111In-containing CHEMS/DOPE/PEG-PE liposomes injected intravenously into rats has pharmacokinetic parameters similar to control, non-pH-sensitive, sterically stabilized CHEMS/distearoylphosphatidylcholine/PEG-PE liposomes. In contrast, regular pH-sensitive liposomes lacking the PEG-PE component are cleared rapidly. Sterically stabilized pH-sensitive liposomes may therefore be useful for the intracellular delivery in vivo of highly negatively charged molecules such as genes, antisense oligonucleotides, and ribozymes for the treatment of various diseases.
Abstract The kinetics of oxidation of d-mannose, 2-deoxy-d-glucose, and d-glucose by glucose oxidase from Penicillium notatum has been studied in the pH range from 3 to 8 at 25°, in the presence of 0.2 m KCl. The pH dependence of the individual steps in the catalytic mechanism was determined by stopped flow spectrophotometric measurements of each half-reaction, in conjunction with conventional steady state kinetic measurements of the over-all reaction. The following scheme, originally deduced by Gibson, Swoboda, and Massey (J. Biol. Chem., 239, 3927 (1964)) for the enzyme from Aspergillus niger at pH 5.6 and 25°, was found to accommodate the results at any value of pH in the range examined. [see PDF for equation] where Eo, Er, S, and P are, respectively, oxidized enzyme, reduced enzyme, substrate, and product. The pH dependence and other characteristics of each step in turn are as follows. 1. The pH profile for k1 is sigmoid, and indicates that the combination of substrate with Eo is dependent upon a basic group (pK1 = 5.00 for mannose and glucose; pK1 = 5.35 for 2-deoxyglucose) in the enzyme. There is a small solvent deuterium isotope effect on k1. Halides have a specific effect on pK1, causing it to increase markedly, but have no effect on k1. 2. Flavin reduction, controlled by k2 and measured with 2-deoxyglucose, is relatively insensitive to pH in the range from 3 to 8. Halides also specifically decrease the rate of flavin reduction. 3. The pH profile for k4 is sigmoid and indicates that the combination of O2 with Er is dependent upon an acidic group (pK4 = 6.90) in the enzyme. 4. The pH profile for k5 is bell shaped and indicates that this terminal, first order process (which may consist of more than one step) is dependent upon an acidic (pK'5 = 7.40) and a basic (pK5 = 4.10) group in the enzyme. Based on these findings, a kinetic scheme is presented which accounts for the pH dependence of the steady state velocity of oxidation of the three sugars in the pH range from 3 to 8. Analogue simulation of the partition of the enzyme between oxidized and reduced forms during turnover at different values of pH, with experimentally determined values of acid dissociation and rate constants, agreed with turnover patterns obtained in stopped flow spectrophotometric experiments at 450 mµ.
The passive permeability of isolated chromaffin vesicles to H+ and the internal pH of the vesicles under various conditions were measured. Potentiometric measurements of K+ and H+ fluxes in the presence of selected ionophores and uncouplers indicated that the membrane is highly impermeable to both protons and potassium. deltapH across the chromaffin granule membrane was measured by [14C]methylamine distribution. At pH 6.85, The deltapH WAS 1.16 WITH THE INTRAVESICULAR SPACE BEING FOUND ACIDIC. Varying the external pH produced an equivalent change in the deltapH, WITH EXTRAPOLATION TO ZERO DEltapH yielding a value of pH 5.5, WHICH IS TAKEN AS AN INDICATION OF THE PH of the intravesicular space. The pH gradient could be enhanced or collapsed by the addition of ionophores and uncouplers under varying ionic conditions. deltapH was constant for granules suspended in various ionic media, suggesting that the deltapH did not arise secondarily due to the establishment of a Donnan equilibrium. The significance of the proton impermeability and deltapH is discussed in terms of regulation of the uptake and storage of catecholamines in bovine chromaffin granules.