Electron spin resonance evidence for the formation of free radicals in plants exposed to ozone

Electron spin resonance (ESR) spectroscopy was used to demonstrate that free radicals are formed in O₃-fumigated plant leaves prior to the formation of visible leaf injury. ESR signals with a g-value of 2.0037 to 2.0043, were observed in pea ( Pisum sativum L. cv. Feltham first) and bean ( Phaseolus vulgaris L. cv. Pinto) plants that had been fumigated for 4 h with 70–300 nl l⁻¹ of ozone after they had been treated with the spin-trap N- t -butyl-α-phenylnitrone (PBN). The size of the ESR signals increased with the concentration of ozone used but the nature of the trapped radicals could not be identified. However, further experiments using an inhibitor of ethylene biosynthesis, arninoethoxyvinyl glycine (AVG), showed that the reaction between ozone and ethylene is the cause for ozone toxicity.     

Multidrug resistance evaluation by confocal microscopy in primary urothelial cancer explant colonies

Assessing functional multidrug resistance (MDR) status in clinical biopsy material using drug autofluorescence has potential applications to clinical management. The small size of many cystoscopy specimens has led us to develop, as an alternative to flow cytometry, a protocol for studying epirubicin accumulation in adherent colonies of primary bladder cancer cells viewed live andin situ by confocal microscopy. The limitations to quantitation inherent in this technique are compensated for by preservation of cellular organisation and the elimination of non-malignant cells. Biopsy material is disaggregated and explanted into culture-grade petri dishes. After incubation for three to seven days plaques of epithelial cells have developed. Classical patterns of sensitive and resistant drug distribution are observed. Cells of the rolled edges of the colony accumulate more drug than those of the inner epithelial monolayer. Some central areas of larger colonies give the appearance of drug arrested at the intercellular junctions to give a fenestrated pattern. These observations contribute to the understanding of mechanisms in MDR as well as forming the basis for a clinical urological MDR evaluation protocol.     

Immune network behavior—II. From oscillations to chaos and stationary states

Two types of behavior have been previously reported in models of immune networks. The typical behavior of simple models, which involve B cells only, is stationary behavior involving several steady states. Finite amplitude perturbations may cause the model to switch between different equilibria. The typical behavior of more realistic models, which involve both B cells and antibody, consists of autonomous oscillations and/or chaos. While stationary behavior leads to easy interpretations in terms of idiotypic memory, oscillatory behavior seems to be in better agreement with experimental data obtained in unimmunized animals. Here we study a series of models of the idiotypic interaction between two B cell clones. The models differ with respect to the incorporation of antibodies, B cell maturation and compartmentalization. The most complicated model in the series has two realistic parameter regimes in which the behavior is respectively stationary and chaotic. The stability of the equilibrium states and the structure and interactions of the stable and unstable manifolds of the saddle-type equilibria turn out to be factors influencing the model's behavior. Whether or not the model is able to attain any form of sustained oscillatory behavior, i.e. limit cycles or chaos, seems to be determined by (global) bifurcations involving the stable and unstable manifolds of the equilibrium states. We attempt to determine whether such behavior should be expected to be attained from reasonable initial conditions by incorporating an immune response to an antigen in the model. A comparison of the behavior of the model with experimental data from the literature provides suggestions for the parameter regime in which the immune system is operating.     

Sequence and structural homology among membrane-associated domains of CFTR and certain transporter proteins

A sequence comparison of the two membrane-associated (MA) domains of the cystic fibrosis transmembrane conductance regulator (CFTR), multidrug resistance transporter (MDR), and -factor pheromone export system (STE6) proteins, each of which are believed to contain a total of 12 transmembrane (TM) segments, reveals significant amino acid homology and length conservation in the loop regions that connect individual TM sequences. Similar structural homology is observed between these proteins, hemolysin B (HLYB) and the major histocompatibility-linked peptide transporter, HAM1, the latter two which contain a single MA domain composed of six TM segments. In addition, there are specific sequences that are conserved within the TM segments of the five different membrane proteins. This observation suggests that the folding topologies of the MA domains of MDR, STE6, and CFTR in the plasma membrane are likely to be very similar. The sequence analysis also reveals that there are three characteristic motifs (a pair of aromatic residues, LTLXXXXXXP and GXXL) that are conserved in MDR, STE6, HLYB, HAM1, but not in CFTR. We propose that although CFTR may be evolutionarily related to these other membrane proteins, it belongs to a separate subclass.     

Surveying nonvisual arrestins reveals allosteric interactions between functional sites

Arrestins are important scaffolding proteins that are expressed in all vertebrate animals. They regulate cell-signaling events upon binding to active G-protein coupled receptors (GPCR) and trigger endocytosis of active GPCRs. While many of the functional sites on arrestins have been characterized, the question of how these sites interact is unanswered. We used anisotropic network modeling (ANM) together with our covariance compliment techniques to survey all the available structures of the nonvisual arrestins to map how structural changes and protein-binding affect their structural dynamics. We found that activation and clathrin binding have a marked effect on arrestin dynamics, and that these dynamics changes are localized to a small number of distant functional sites. These sites include α-helix 1, the lariat loop, nuclear localization domain, and the C-domain β-sheets on the C-loop side. Our techniques suggest that clathrin binding and/or GPCR activation of arrestin perturb the dynamics of these sites independent of structural changes.     

Wording, Meaning, and Linguistic Ideology

Two seemingly disparate areas of English language structure—the grammar of reported speech and of textual cohesion—are functionally related in that both entail a distinction between "wording" and "meaning." This is consistent with the Western ideological disjunction between language and reality, talk and action. Neither these language structures nor this linguistic ideology are found among the Ngarinyin people of northwestern Australia, suggesting a Whorfian hypothesis about their possible interrelationship.