Multiple molecular forms of xanthine dehydrogenase and related enzymes. IV. The relationship of aldehyde oxidase to xanthine dehydrogenase

Variants of the enzyme aldehyde oxidase in Drosophila melanogaster are described. In addition to electrophoretic variants, a mutant that causes low levels of the enzyme has been found by screening more than 80 strains for aldehyde oxidase levels. The locus of the mutation maps on the third chromosome near lpo and aldox. The existence of the ry, lpo, and aldox mutants and of the new mutant indicates that xanthine dehydrogenase, pyridoxal oxidase, and aldehyde oxidase are under a separate genetic control, in addition to a common genetic control by ma-l and lxd. The genetic separation is shown to be accompanied by physical separation of the enzymes with DEAE-cellulose column chromatography and (NH ₄)₂SO₄fractionation. Further data on the metabolism of aldehydes by xanthine dehydrogenase and aldehyde oxidase are presented. Although xanthine dehydrogenase requires NAD or a similar cofactor to metabolize purine and pteridine substrates, aldehyde oxidase oxidizes salicylaldehyde to salicylic acid without dissociable cofactors and with the uptake of oxygen.This work was supported in part by Research Grant GM-08202, by a Predoctoral Fellowship (J.C.) and a Genetics Training Grant (J.C. and E.D.), and by a Research Career Development Award (E.G.), all from the National Institutes of Health. Part of this work was submitted by J.C. to the University of North Carolina at Chapel Hill in partial fulfillment of the degree of Doctor of Philosophy.     

Natriuretic peptides modify <Emphasis Type="Italic">Pseudomonas fluorescens</Emphasis> cytotoxicity by regulating cyclic nucleotides and modifying LPS structure

Background  

Nervous tissues express various communication molecules including natriuretic peptides, i.e. Brain Natriuretic Peptide (BNP) and C-type Natriuretic Peptide (CNP). These molecules share structural similarities with cyclic antibacterial peptides. CNP and to a lesser extent BNP can modify the cytotoxicity of the opportunistic pathogen Pseudomonas aeruginosa. The psychrotrophic environmental species Pseudomonas fluorescens also binds to and kills neurons and glial cells, cell types that both produce natriuretic peptides. In the present study, we investigated the sensitivity of Pseudomonas fluorescens to natriuretic peptides and evaluated the distribution and variability of putative natriuretic peptide-dependent sensor systems in the Pseudomonas genus.     

Involvement of a phospholipase C in the hemolytic activity of a clinical strain of <Emphasis Type="Italic">Pseudomonas fluorescens</Emphasis>

Background  

Pseudomonas fluorescens is a ubiquitous Gram-negative bacterium frequently encountered in hospitals as a contaminant of injectable material and surfaces. This psychrotrophic bacterium, commonly described as unable to grow at temperatures above 32°C, is now considered non pathogenic. We studied a recently identified clinical strain of P. fluorescens biovar I, MFN1032, which is considered to cause human lung infection and can grow at 37°C in laboratory conditions.     

Computational study of the putative active form of protein Z (PZa): sequence design and structural modeling

Although protein Z (PZ) has a domain arrangement similar to the essential coagulation proteins FVII, FIX, FX, and protein C, its serine protease (SP)-like domain is incomplete and does not exhibit proteolytic activity. We have generated a trial sequence of putative activated protein Z (PZa) by identifying amino acid mutations in the SP-like domain that might reasonably resurrect the serine protease catalytic activity of PZ. The structure of the activated form was then modeled based on the proposed sequence using homology modeling and solvent-equilibrated molecular dynamics simulations. In silico docking of inhibitors of FVIIa and FXa to the putative active site of equilibrated PZa, along with structural comparison with its homologous proteins, suggest that the designed PZa can possibly act as a serine protease.     

Substituted benzothiadizine inhibitors of Hepatitis C virus polymerase

The synthesis and optimisation of HCV NS5B polymerase inhibitors with improved potency versus the existing compound 1 is described. Substitution in the benzothiadiazine portion of the molecule, furnishing improvement in potency in the high protein Replicon assay, is highlighted, culminating in the discovery of 12h, a highly potent oxyacetamide derivative.     

Colonisation and mass rearing: learning from others

Mosquitoes, just as other insects produced for the sterile insect technique (SIT), are subjected to several unnatural processes including laboratory colonisation and large-scale factory production. After these processes, sterile male mosquitoes must perform the natural task of locating and mating with wild females. Therefore, the colonisation and production processes must preserve characters necessary for these functions. Fortunately, in contrast to natural selection which favours a suite of characteristics that improve overall fitness, colonisation and production practices for SIT strive to maximize only the few qualities that are necessary to effectively control populations.However, there is considerable uncertainty about some of the appropriate characteristics due to the lack of data. Development of biological products for other applications suggest that it is possible to identify and modify competitiveness characteristics in order to produce competitive mass produced sterile mosquitoes. This goal has been pursued - and sometimes achieved - by mosquito colonisation, production, and studies that have linked these characteristics to field performance. Parallels are drawn to studies in other insect SIT programmes and aquaculture which serve as vital technical reference points for mass-production of mosquitoes, most of whose development occurs - and characteristics of which are determined - in an aquatic environment. Poorly understood areas that require further study are numerous: diet, mass handling and genetic and physiological factors that influence mating competitiveness. Compromises in such traits due to demands to increase numbers or reduce costs, should be carefully considered in light of the desired field performance.     

Ecophysiological responses of salt cedar (Tamarix spp. L.) to the northern tamarisk beetle (Diorhabdacarinulata Desbrochers) in a controlled environment

The northern tamarisk beetle (Diorhabda carinulata Desbrochers) was released in several western states as a biocontrol agent to suppress Tamarix spp. L. which has invaded riparian ecosystems; however, effects of beetle herbivory on Tamarix physiology are largely undocumented and may have ecosystem ramifications. Herbivory by this insect produces discoloration of leaves and premature leaf drop in these ecosystems, yet the cause of premature leaf drop and the effects of this leaf drop are still unknown. Insect herbivory may change leaf photosynthesis and respiration and may affect a plant’s ability to regulate water loss and increase water stress. Premature leaf drop may affect plant tissue chemistry and belowground carbon allocation. We conducted a greenhouse experiment to understand how Tamarix responds physiologically to adult beetle and larvae herbivory and to determine the proximate cause of premature leaf drop. We hypothesized that plants experiencing beetle herbivory would have greater leaf and root respiration rates, greater photosynthesis, increased water stress, inefficient leaf nitrogen retranslocation, lower root biomass and lower total non-structural carbohydrates in roots. Insect herbivory reduced photosynthesis rates, minimally affected respiration rates, but significantly increased water loss during daytime and nighttime hours and this produced increased water stress. The proximate cause for premature leaf drop appears to be desiccation. Plants exposed to herbivory were inefficient in their retranslocation of nitrogen before premature leaf drop. Root biomass showed a decreasing trend in plants subjected to herbivory. Stress induced by herbivory may render these trees less competitive in future growing seasons.     

Measuring succession: methods for establishing long-term vegetation monitoring sites

Successional stages are often characterized by dominant plant species (species with the highest cover) and their effect on the structure and function of an area through time. However, the plant species determining the ecosystem properties and plant community dynamics may not be the dominant, especially when it is exotic. Understanding plant community dynamics in ecosystems that are uncharacterized and/or affected by invasive plant species requires a data-driven approach and proper placement of monitoring plots. To generate robust datasets on vegetation change through time, monitoring plot placement must consider the scale of ecological variation for both vegetation and soils and plots would ideally be replicated within similar ecological site types to quantify the consistency of successional transitions. We characterized soil and vegetation across and within seven floodplains affected by Russian olive (Elaeagnus angustifolia L.) along the Yellowstone River in southeastern Montana, USA. Using modern Classification and Regression Trees (CART) and multivariate net differentiation, we identified five distinct plant community types, or classes, characterized by their tertiary woody plant cover, not the primary species, Russian olive. Our findings indicate that Russian olive communities differ across space, and these riparian areas can be classified into distinct plant community types. Characterizing plant community types via this analytical approach should allow practitioners to modify management decisions and forecast succession within relevant plant communities.     

Focus on Weed Control: Natural Compounds as Next-Generation Herbicides

Herbicides with new modes of action (MOAs) are badly needed due to the rapidly evolving resistance to commercial herbicides, but a new MOA has not been introduced in over 20 years. The greatest pest management challenge for organic agriculture is the lack of effective natural product herbicides. The structural diversity and evolved biological activity of natural phytotoxins offer opportunities for the development of both directly used natural compounds and synthetic herbicides with new target sites based on the structures of natural phytotoxins. Natural phytotoxins are also a source for the discovery of new herbicide target sites that can serve as the focus of traditional herbicide discovery efforts. There are many examples of strong natural phytotoxins with MOAs other than those used by commercial herbicides, which indicates that there are molecular targets of herbicides that can be added to the current repertoire of commercial herbicide MOAs.The evolutionary forces driving the survival of species include chemical interactions between organisms, which function in positive interactions such as mutualistic and symbiotic relationships and negative interactions such as competitive and parasitic relationships. These processes have led to the emergence of novel secondary metabolic pathways (often through gene duplication), producing a vast array of structurally diverse and biologically active molecules (Moore and Purugganan, 2005; Ober, 2005; Flagel and Wendel, 2009; Jiang et al., 2013). This evolutionary process is similar to a high-throughput screen. However, unlike conventional in vitro screens, which test many compounds on a single biochemical target over a very short period of time, this natural high-throughput process selects molecules based on their whole-organism activities, involving numerous chemical interactions between countless organisms and target sites over millions of years. To date, approximately 200,000 secondary metabolites have been identified (Tulp and Bohlin, 2005), with many more expected to be discovered. Few of these compounds have been examined for phytotoxicity, and the modes or mechanisms of action (MOAs) of even fewer known phytotoxins have been elucidated.The negative chemical interactions between organisms are often characterized using anthropomorphic language, such as chemical warfare, referring to the production of phytotoxins used by plant pathogens to invade their host plants (Maor and Shirasu, 2005), and the novel weapons hypothesis, which is associated with the chemical-based advantage of some invasive plant species over native plant populations (Callaway and Aschehoug, 2000; Callaway and Ridenour, 2004; Callaway and Maron, 2006; Cappuccino and Arnason, 2006; Callaway et al., 2008). While simplistic, this terminology illustrates how these toxin-based interactions exploit biochemical weaknesses between an organism and its host or enemy/competitor to enhance its own survival (Verhoeven et al., 2009). In fact, these interactions can even be multitrophic, such as when exotic plants enhance their invasiveness by promoting the growth of certain native soil pathogens noxious to native plants (Mangla et al., 2008; Barto et al., 2011).As humans evolved from a nomadic hunter-gatherer subsistence existence to an agricultural lifestyle, they learned to utilize certain biologically active secondary metabolites to manage agricultural pests. Indeed, the concept that nature is an excellent source of natural pesticides is captured in the following ancient Lithica poem (circa 400 B.C.): “All the pests that out of earth arise, the earth itself the antidote supplies” (Ibn et al., 1781). Less than a century later, Greek and Roman treatises described practices to control agricultural pests that include the use of essential oils. Similar documents are found in Chinese literature, such as a survey describing plant species used to control plant pests (Yang and Tang, 1988). The mid-20th century ushered in the use of synthetic pesticides, which have revolutionized agriculture. Like pharmaceuticals (Harvey, 1999, 2008; Newman and Cragg, 2012), many pesticides are based on natural compounds. However, natural products have not played a major role in herbicide discovery (Copping and Duke, 2007; Hüter, 2011).