RESUMEN
Radical S-adenosylmethionine (SAM) enzymes use a site-differentiated [4Fe-4S] cluster and SAM to initiate radical reactions through liberation of the 5'-deoxyadenosyl (5'-dAdoâ¢) radical. They form the largest enzyme superfamily, with more than 700,000 unique sequences currently, and their numbers continue to grow as a result of ongoing bioinformatics efforts. The range of extremely diverse, highly regio- and stereo-specific reactions known to be catalyzed by radical SAM superfamily members is remarkable. The common mechanism of radical initiation in the radical SAM superfamily is the focus of this review. Most surprising is the presence of an organometallic intermediate, Ω, exhibiting an Fe-C5'-adenosyl bond. Regioselective reductive cleavage of the SAM S-C5' bond produces 5'-dAdo⢠to form Ω, with the regioselectivity originating in the Jahn-Teller effect. Ω liberates the free 5'-dAdo⢠as the catalytically active intermediate through homolysis of the Fe-C5' bond, in analogy to Co-C5' bond homolysis in B12, which was once viewed as biology's choice of radical generator.
Asunto(s)
Proteínas Hierro-Azufre , S-Adenosilmetionina , S-Adenosilmetionina/química , Proteínas Hierro-Azufre/genética , Proteínas Hierro-Azufre/químicaRESUMEN
The past decade has seen impressive advances in understanding the biosynthesis of ribosomally synthesized and posttranslationally modified peptides (RiPPs). One of the most common modifications found in these natural products is macrocyclization, a strategy also used by medicinal chemists to improve metabolic stability and target affinity and specificity. Another tool of the peptide chemist, modification of the amides in a peptide backbone, has also been observed in RiPPs. This review discusses the molecular mechanisms of biosynthesis of a subset of macrocyclic RiPP families, chosen because of the unusual biochemistry involved: the five classes of lanthipeptides (thioether cyclization by Michael-type addition), sactipeptides and ranthipeptides (thioether cyclization by radical chemistry), thiopeptides (cyclization by [4+2] cycloaddition), and streptide (cyclization by radical C-C bond formation). In addition, the mechanisms of backbone amide methylation, backbone epimerization, and backbone thioamide formation are discussed, as well as an unusual route to small molecules by posttranslational modification.
Asunto(s)
Péptidos , Procesamiento Proteico-Postraduccional , Secuencia de Aminoácidos , Humanos , Péptidos/química , Sulfuros/química , Sulfuros/metabolismoRESUMEN
Sulfonates include diverse natural products and anthropogenic chemicals and are widespread in the environment. Many bacteria can degrade sulfonates and obtain sulfur, carbon, and energy for growth, playing important roles in the biogeochemical sulfur cycle. Cleavage of the inert sulfonate C-S bond involves a variety of enzymes, cofactors, and oxygen-dependent and oxygen-independent catalytic mechanisms. Sulfonate degradation by strictly anaerobic bacteria was recently found to involve C-S bond cleavage through O2-sensitive free radical chemistry, catalyzed by glycyl radical enzymes (GREs). The associated discoveries of new enzymes and metabolic pathways for sulfonate metabolism in diverse anaerobic bacteria have enriched our understanding of sulfonate chemistry in the anaerobic biosphere. An anaerobic environment of particular interest is the human gut microbiome, where sulfonate degradation by sulfate- and sulfite-reducing bacteria (SSRB) produces H2S, a process linked to certain chronic diseases and conditions.
Asunto(s)
Liasas de Carbono-Carbono/metabolismo , Microbioma Gastrointestinal/fisiología , Ácidos Sulfónicos/metabolismo , Acetiltransferasas/química , Acetiltransferasas/metabolismo , Alcanosulfonatos/metabolismo , Anaerobiosis , Bacterias/metabolismo , Liasas de Carbono-Carbono/química , Glicina/metabolismo , Humanos , Sulfuro de Hidrógeno/metabolismo , Ácido Isetiónico/metabolismo , Microbiota/fisiología , Taurina/metabolismoRESUMEN
The activation of G proteins by G protein-coupled receptors (GPCRs) underlies the majority of transmembrane signaling by hormones and neurotransmitters. Recent structures of GPCR-G protein complexes obtained by crystallography and cryoelectron microscopy (cryo-EM) reveal similar interactions between GPCRs and the alpha subunit of different G protein isoforms. While some G protein subtype-specific differences are observed, there is no clear structural explanation for G protein subtype-selectivity. All of these complexes are stabilized in the nucleotide-free state, a condition that does not exist in living cells. In an effort to better understand the structural basis of coupling specificity, we used time-resolved structural mass spectrometry techniques to investigate GPCR-G protein complex formation and G-protein activation. Our results suggest that coupling specificity is determined by one or more transient intermediate states that serve as selectivity filters and precede the formation of the stable nucleotide-free GPCR-G protein complexes observed in crystal and cryo-EM structures.
Asunto(s)
Proteínas de Unión al GTP/química , Complejos Multienzimáticos/química , Receptores Acoplados a Proteínas G/química , Animales , Bovinos , Microscopía por Crioelectrón , Cristalografía por Rayos X , Humanos , Complejos Multienzimáticos/ultraestructura , Estructura Cuaternaria de Proteína , RatasRESUMEN
S-adenosylmethionine (AdoMet) has been referred to as both "a poor man's adenosylcobalamin (AdoCbl)" and "a rich man's AdoCbl," but today, with the ever-increasing number of functions attributed to each cofactor, both appear equally rich and surprising. The recent characterization of an organometallic species in an AdoMet radical enzyme suggests that the line that differentiates them in nature will be constantly challenged. Here, we compare and contrast AdoMet and cobalamin (Cbl) and consider why Cbl-dependent AdoMet radical enzymes require two cofactors that are so similar in their reactivity. We further carry out structural comparisons employing the recently determined crystal structure of oxetanocin-A biosynthetic enzyme OxsB, the first three-dimensional structural data on a Cbl-dependent AdoMet radical enzyme. We find that the structural motifs responsible for housing the AdoMet radical machinery are largely conserved, whereas the motifs responsible for binding additional cofactors are much more varied.
Asunto(s)
S-Adenosilmetionina/metabolismo , Vitamina B 12/metabolismo , Animales , Sitios de Unión , Coenzimas/química , Coenzimas/metabolismo , Electroquímica , Enzimas/química , Enzimas/metabolismo , Radicales Libres/química , Radicales Libres/metabolismo , Humanos , Modelos Moleculares , Estructura Molecular , S-Adenosilmetionina/química , Vitamina B 12/análogos & derivados , Vitamina B 12/químicaRESUMEN
Nitrogenase is a versatile metalloenzyme that is capable of catalyzing two important reactions under ambient conditions: the reduction of nitrogen (N2) to ammonia (NH3), a key step in the global nitrogen cycle; and the reduction of carbon monoxide (CO) and carbon dioxide (CO2) to hydrocarbons, two reactions useful for recycling carbon waste into carbon fuel. The molybdenum (Mo)- and vanadium (V)-nitrogenases are two homologous members of this enzyme family. Each of them contains a P-cluster and a cofactor, two high-nuclearity metalloclusters that have crucial roles in catalysis. This review summarizes the progress that has been made in elucidating the biosynthetic mechanisms of the P-cluster and cofactor species of nitrogenase, focusing on what is known about the assembly mechanisms of the two metalloclusters in Mo-nitrogenase and giving a brief account of the possible assembly schemes of their counterparts in V-nitrogenase, which are derived from the homology between the two nitrogenases.
Asunto(s)
Azotobacter vinelandii/enzimología , Proteínas Bacterianas/metabolismo , Coenzimas/metabolismo , Molibdeno/metabolismo , Nitrogenasa/metabolismo , Subunidades de Proteína/metabolismo , Secuencia de Aminoácidos , Amoníaco/química , Amoníaco/metabolismo , Azotobacter vinelandii/genética , Proteínas Bacterianas/química , Proteínas Bacterianas/genética , Biocatálisis , Dióxido de Carbono/química , Dióxido de Carbono/metabolismo , Monóxido de Carbono/química , Monóxido de Carbono/metabolismo , Coenzimas/química , Hierro/química , Hierro/metabolismo , Molibdeno/química , Nitrógeno/química , Nitrógeno/metabolismo , Nitrogenasa/química , Nitrogenasa/genética , Oxidación-Reducción , Subunidades de Proteína/química , Subunidades de Proteína/genética , Alineación de Secuencia , Homología de Secuencia de Aminoácido , Vanadio/química , Vanadio/metabolismoRESUMEN
The free radical nitric oxide (·NO) is a key mediator in different physiological processes such as vasodilation, neurotransmission, inflammation, and cellular immune responses, and thus preserving its bioavailability is essential. In several disease conditions, superoxide radical (O2·-) production increases and leads to the rapid "inactivation" of ·NO by a diffusion-controlled radical termination reaction that yields a potent and short-lived oxidant, peroxynitrite. This reaction not only limits ·NO bioavailability for physiological signal transduction but also can divert and switch the biochemistry of ·NO toward nitrooxidative processes. Indeed, since the early 1990s peroxynitrite (and its secondary derived species) has been linked to the establishment and progression of different acute and chronic human diseases and also to the normal aging process. Here, we revisit an earlier and classical review on the role of peroxynitrite in human physiology and pathology (Pacher P, Beckman J, Liaudet L. Physiol Rev 87: 315-424, 2007) and further integrate, update, and interpret the accumulated evidence over 30 years of research. Innovative tools and approaches for the detection, quantitation, and sub- or extracellular mapping of peroxynitrite and its secondary products (e.g., protein 3-nitrotyrosine) have allowed us to unambiguously connect the complex biochemistry of peroxynitrite with numerous biological outcomes at the physiological and pathological levels. Furthermore, our current knowledge of the ·NO/O2·- and peroxynitrite interplay at the cell, tissue, and organ levels is assisting in the discovery of therapeutic interventions for a variety of human diseases.
Asunto(s)
Ácido Peroxinitroso , Superóxidos , Biología , Humanos , Óxido Nítrico/metabolismo , Ácido Peroxinitroso/metabolismoRESUMEN
Archaea produce unique membrane-spanning lipids (MSLs), termed glycerol dialkyl glycerol tetraethers (GDGTs), which aid in adaptive responses to various environmental challenges. GDGTs can be modified through cyclization, cross-linking, methylation, hydroxylation, and desaturation, resulting in structurally distinct GDGT lipids. Here, we report the identification of radical SAM proteins responsible for two of these modifications-a glycerol monoalkyl glycerol tetraether (GMGT) synthase (Gms), responsible for covalently cross-linking the two hydrocarbon tails of a GDGT to produce GMGTs, and a GMGT methylase (Gmm), capable of methylating the core hydrocarbon tail. Heterologous expression of Gms proteins from various archaea in Thermococcus kodakarensis results in the production of GMGTs in two isomeric forms. Further, coexpression of Gms and Gmm produces mono- and dimethylated GMGTs and minor amounts of trimethylated GMGTs with only trace GDGT methylation. Phylogenetic analyses reveal the presence of Gms homologs in diverse archaeal genomes spanning all four archaeal superphyla and in multiple bacterial phyla with the genetic potential to synthesize fatty acid-based MSLs, demonstrating that GMGT production may be more widespread than previously appreciated. We demonstrate GMGT production in three Gms-encoding archaea, identifying an increase in GMGTs in response to elevated temperature in two Archaeoglobus species and the production of GMGTs with up to six rings in Vulcanisaeta distributa. The occurrence of such highly cyclized GMGTs has been limited to environmental samples and their detection in culture demonstrates the utility of combining genetic, bioinformatic, and lipid analyses to identify producers of distinct archaeal membrane lipids.
Asunto(s)
Archaea , Proteínas Arqueales , Filogenia , Proteínas Arqueales/metabolismo , Proteínas Arqueales/genética , Archaea/metabolismo , Archaea/genética , Thermococcus/metabolismo , Thermococcus/genética , Éteres de Glicerilo/metabolismo , Lípidos de la Membrana/metabolismo , Lípidos de la Membrana/biosíntesisRESUMEN
Integrating reactive radicals into membranes that resemble biological membranes has always been a pursuit for simultaneous organics degradation and water filtration. In this research, we discovered that a radical polymer (RP) that can directly trigger the oxidative degradation of sulfamethozaxole (SMX). Mechanistic studies by experiment and density functional theory simulations revealed that peroxyl radicals are the reactive species, and the radicals could be regenerated in the presence of O2. Furthermore, an interpenetrating RP network membrane consisting of polyvinyl alcohol and the RP was fabricated to demonstrate the simultaneous filtration of large molecules in the model wastewater stream and the degradation of ~ 85% of SMX with a steady permeation flux. This study offers valuable insights into the mechanism of RP-triggered advanced oxidation processes and provides an energy-efficient solution for the degradation of organic compounds and water filtration in wastewater treatment.
RESUMEN
Homogenous advanced oxidation processes (AOPs) based on transition metal catalysts toward the activation of H2O2 to hydroxyl radical (â¢OH) have been widely applied to organic pollutants removal, such as Fenton and Fenton-like processes. These transition metal catalysts mostly flocculate as the pH increases. It's worth noting that the formed transition metal flocs are complex heterogeneous aggregations with active substances, providing diverse reaction spaces and interfaces. However, it is a challenge to distinguish the roles of transition metal flocs in the organic pollutants removal from homogeneous catalytic reactions. Herein, we unveiled a pathway for the long-lasting removal of organic pollutants via Cr flocs adsorbed with â¢OH (HOâ¢-Cr flocs) using a stepwise method. First, adsorbed â¢OH (â¢OHads) within the HOâ¢-Cr flocs was proved to be the active site forming hydrogen bond (H-bond) and van der Waals force with organic pollutants. Then, the presence of switchable electron transfer between Cr and OH groups within the HOâ¢-Cr flocs was revealed, contributing to the persistent existence of â¢OHads and consequently ensuring the long-lasting organics removal. Further, this removal pathway of organic pollutants was confirmed during the leather wastewater treatment. These findings will complement a different pathway for organic pollutants removal via transition metal flocs and extend the lifetime of homogeneous AOPs based on transition metal catalysts, providing significant implications for their design and optimization.
RESUMEN
Emerging contaminants (EC) distributed on surfaces in the environment can be oxidized by gas phase species (top-down) or by oxidants generated by the underlying substrate (bottom-up). One class of EC is the neonicotinoid (NN) pesticides that are widely distributed in air, water, and on plant and soil surfaces as well as on airborne dust and building materials. This study investigates the OH oxidation of the systemic NN pesticide acetamiprid (ACM) at room temperature. ACM on particles and as thin films on solid substrates were oxidized by OH radicals either from the gas phase or from an underlying TiO2 or NaNO2 substrate, and for comparison, in the aqueous phase. The site of OH attack is both the secondary >CH2 group as well as the primary -CH3 group attached to the tertiary amine nitrogen, with the latter dominating. In the case of top-down oxidation of ACM by gas phase OH radicals, addition to the -CN group also occurs. Major products are carbonyls and alcohols, but in the presence of sufficient water, their hydrolyzed products dominate. Kinetics measurements show ACM is more reactive toward gas phase OH radicals than other NN nitroguanidines, with an atmospheric lifetime of a few days. Bottom-up oxidation of ACM on TiO2 exposed to sunlight outdoors (temperatures were above 30 °C) was also shown to occur and is likely to be competitive with top-down oxidation. These findings highlight the different potential oxidation processes for EC and provide key data for assessing their environmental fates and toxicologies.
RESUMEN
It is well-known that highly reactive hydroxyl radicals (HOâ¢) can be produced by the classic Fenton system and our recently discovered haloquinone/H2O2 system, but rarely from thiol-derivatives. Here, we found, unexpectedly, that HO⢠can be generated from H2O2 and thiourea dioxide (TUO2), a widely used and environmentally friendly bleaching agent. A carbon-centered radical and sulfite were detected and identified as the transient intermediates, and urea and sulfate as the final products, with the complementary application of electron spin-trapping, oxygen-18 isotope labeling coupled with HPLC/MS analysis. Density functional theory calculations were conducted to further elucidate the detailed pathways for HO⢠production. Taken together, we proposed that the molecular mechanism for HO⢠generation by TUO2/H2O2: TUO2 tautomerizes from sulfinic acid into ketone isomer (TUO2-K) through proton transfer, then a nucleophilic addition of H2O2 on the S atom of TUO2-K, forming a S-hydroperoxide intermediate TUO2-OOH, which dissociates homolytically to produce HOâ¢. Our findings represent the first experimental and computational study on an unprecedented new molecular mechanism of HO⢠production from simple thiol-derived sulfinic acids, which may have broad chemical, environmental, and biomedical significance for future research on the application of the well-known bleaching agent and its analogs.
RESUMEN
Ribonucleotide reductases (RNRs) are essential enzymes that catalyze the de novo transformation of nucleoside 5'-di(tri)phosphates [ND(T)Ps, where N is A, U, C, or G] to their corresponding deoxynucleotides. Despite the diversity of factors required for function and the low sequence conservation across RNRs, a unifying apparatus consolidating RNR activity is explored. We combine aspects of the protein subunit simplicity of class II RNR with a modified version of Escherichia coli class la photoRNRs that initiate radical chemistry with light to engineer a mimic of a class II enzyme. The design of this RNR involves fusing a truncated form of the active site containing α subunit with the functionally important C-terminal tail of the radical-generating ß subunit to render a chimeric RNR. Inspired by a recent cryo-EM structure, a [Re] photooxidant is located adjacent to Y356[ß], which is an essential component of the radical transport pathway in class I RNRs. Combination of this RNR photochimera with cytidine diphosphate (CDP), adenosine triphosphate (ATP), and light resulted in the generation of Y356⢠along with production of deoxycytidine diphosphate (dCDP) and cytosine. The photoproducts reflect an active site chemistry consistent with both the consensus mechanism of RNR and chemistry observed when RNR is inactivated by mechanism-based inhibitors in the active site. The enzymatic activity of the RNR photochimera in the absence of any ß metallocofactor highlights the adaptability of the 10-stranded αß barrel finger loop to support deoxynucleotide formation and accommodate the design of engineered RNRs.
Asunto(s)
Escherichia coli , Ingeniería de Proteínas , Ribonucleótido Reductasas , Ribonucleótido Reductasas/metabolismo , Ribonucleótido Reductasas/química , Ribonucleótido Reductasas/genética , Ingeniería de Proteínas/métodos , Escherichia coli/genética , Escherichia coli/metabolismo , Dominio Catalítico , Evolución Molecular , Modelos Moleculares , Proteínas de Escherichia coli/metabolismo , Proteínas de Escherichia coli/genética , Proteínas de Escherichia coli/químicaRESUMEN
The therapeutic targeting of ferroptosis requires full understanding of the molecular mechanism of this regulated cell death pathway. While lipid-derived electrophiles (LDEs), including 4-hydroxy-2-nonenal (4-HNE), are important biomarkers of ferroptosis, a functional role for these highly reactive species in ferroptotic cell death execution has not been established. Here, through mechanistic characterization of LDE-detoxification impairment, we demonstrate that LDEs mediate altered protein function during ferroptosis. Applying live cell fluorescence imaging, we first identified that export of glutathione-LDE-adducts through multidrug resistance-associated protein (MRP) channels is inhibited following exposure to a panel of ferroptosis inducers (FINs) with different modes of action (type I-IV FINs erastin, RSL3, FIN56, and FINO2). This channel inhibition was recreated by both initiation of lipid peroxidation and treatment with 4-HNE. Importantly, treatment with radical-trapping antioxidants prevented impaired LDE-adduct export when working with both FINs and lipid peroxidation initiators but not 4-HNE, pinpointing LDEs as the cause of this inhibited MRP activity observed during ferroptosis. Our findings, when combined with reports of widespread LDE alkylation of key proteins following ferroptosis induction, including MRP1, set a precedent for LDEs as critical mediators of ferroptotic cell damage. Lipid hydroperoxide breakdown to form truncated phospholipids and LDEs may fully explain membrane permeabilization and modified protein function downstream of lipid peroxidation, offering a unified explanation of the molecular cell death mechanism of ferroptosis.
Asunto(s)
Aldehídos , Ferroptosis , Peroxidación de Lípido , Ferroptosis/efectos de los fármacos , Humanos , Peroxidación de Lípido/efectos de los fármacos , Aldehídos/farmacología , Aldehídos/metabolismo , Proteínas Asociadas a Resistencia a Múltiples Medicamentos/metabolismo , Glutatión/metabolismoRESUMEN
Plasmodium vivax is the most widespread human malaria parasite, in part because it can form latent liver stages known as hypnozoites after transmission by female anopheline mosquitoes to human hosts. These persistent stages can activate weeks, months, or even years after the primary clinical infection; replicate; and initiate relapses of blood stage infection, which causes disease and recurring transmission. Eliminating hypnozoites is a substantial obstacle for malaria treatment and eradication since the hypnozoite reservoir is undetectable and unaffected by most antimalarial drugs. Importantly, in some parts of the globe where P. vivax malaria is endemic, as many as 90% of P. vivax blood stage infections are thought to be relapses rather than primary infections, rendering the hypnozoite a major driver of P. vivax epidemiology. Here, we review the biology of the hypnozoite and recent discoveries concerning this enigmatic parasite stage. We discuss treatment and prevention challenges, novel animal models to study hypnozoites and relapse, and hypotheses related to hypnozoite formation and activation.
Asunto(s)
Malaria Vivax , Malaria , Animales , Femenino , Hígado/parasitología , Malaria Vivax/tratamiento farmacológico , Malaria Vivax/parasitología , Malaria Vivax/prevención & control , Plasmodium vivax/fisiología , RecurrenciaRESUMEN
Mechanisms occurring at the atomic level are now known to drive processes essential for life, as revealed by quantum effects on biochemical reactions. Some macroscopic characteristics of organisms may thus show an atomic imprint, which may be transferred across organisms and affect their evolution. This possibility is considered here for the first time, with the aim of elucidating the appearance of an animal innovation with an unclear evolutionary origin: migratory behaviour. This trait may be mediated by a radical pair (RP) mechanism in the retinal flavoprotein cryptochrome, providing essential magnetic orientation for migration. Isotopes may affect the performance of quantum processes through their nuclear spin. Here, we consider a simple model and then apply the standard open quantum system approach to the spin dynamics of cryptochrome RP. We changed the spin quantum number (I) and g-factor of hydrogen and nitrogen isotopes to investigate their effect on RP's yield and magnetic sensitivity. Strong differences arose between isotopes with I = 1 and I = 1/2 in their contribution to cryptochrome magnetic sensitivity, particularly regarding Earth's magnetic field strengths (25-65 µT). In most cases, isotopic substitution improved RP's magnetic sensitivity. Migratory behaviour may thus have been favoured in animals with certain isotopic compositions of cryptochrome.
Asunto(s)
Migración Animal , Criptocromos , Animales , Criptocromos/química , Campos Magnéticos , Aves , Isótopos , BiologíaRESUMEN
Synthetic amorphous silica is a common food additive and a popular cosmetic ingredient. Mesoporous silica particles are also widely studied for their potential use in drug delivery and imaging applications because of their unique properties, such as tunable pore sizes, large surfaces areas, and assumed biocompatibility. Such a nanomaterial, when consisting of pure silicon dioxide, is generally considered to be chemically inert, but in this study, we showed that oxidation yields for different compounds were facilitated by simply incubating aqueous solutions with pure silica particles. Three thiol-containing molecules, L-cysteine, glutathione, and D-penicillamine, were studied separately, and it was found that more than 95% of oxidation happened after incubating any of these compounds with mesoporous silica particles in the dark for a day at room temperature. Oxidation increased over incubation time, and more oxidation was found for particles having larger surface areas. For nonporous silica particles at submicron ranges, yields of oxidation were different based on the structures of molecules, correlating with steric hindrance while accessing surfaces. We propose that the silyloxy radical (SiOâ¢) on silica surfaces is what facilitates oxidation. Density functional theory calculations were conducted for total energy changes for reactions between different aqueous species and silicon dioxide surfaces. These calculations identified two most plausible pathways of the lowest energy to generate SiO⢠radicals from water radical cations H2Oâ¢+ and hydroxyl radicals â¢OH, previously known to exist at water interfaces.
RESUMEN
Hate crime is a pervasive problem across societies. Though perpetrators represent a small share of the population, their actions continue in part because they enjoy community support. But we know very little about this wider community of support; existing surveys do not measure whether citizens approve of hate crime. Focusing on Germany, where antiminority violence is entrenched, this paper uses original surveys to provide systematic evidence on the nature and impacts of hate crime support. Employing direct and indirect measures, I find that significant shares of the population support antirefugee hate crime and that the profile of supporters is broad, going much beyond common perpetrator types. I next use a candidate choice experiment to show that this support has disturbing political consequences: among radical right voters, hate crime supporters prefer candidates who endorse using gun violence against refugees. I conclude that a significant number of citizens empower potential perpetrators from the bottom-up and further legitimize hate crime from the top-down by championing violence-promoting political elites.
Asunto(s)
Víctimas de Crimen , Odio , Humanos , Crimen , Violencia , Agresión , Susceptibilidad a Enfermedades , PrejuicioRESUMEN
Night-migratory songbirds have a light-dependent magnetic compass sense, the mechanism of which is thought to depend on the photochemical formation of radical pairs in cryptochrome (Cry) proteins located in the retina. The finding that weak radiofrequency (RF) electromagnetic fields can prevent birds from orienting in the Earth's magnetic field has been regarded as a diagnostic test for this mechanism and as a potential source of information on the identities of the radicals. The maximum frequency that could cause such disorientation has been predicted to lie between 120 and 220 MHz for a flavin-tryptophan radical pair in Cry. Here we show that the magnetic orientation capabilities of Eurasian blackcaps (Sylvia atricapilla) are not affected by RF noise in the frequency bands 140 to 150 MHz and 235 to 245 MHz. From a consideration of its internal magnetic interactions, we argue that RF field effects on a flavin-containing radical-pair sensor should be approximately independent of frequency up to 116 MHz and that birds' sensitivity to RF disorientation should fall by about two orders of magnitude when the frequency exceeds 116 MHz. Taken together with our earlier finding that 75 to 85 MHz RF fields disrupt the magnetic orientation of blackcaps, these results provide compelling evidence that the magnetic compass of migratory birds operates by a radical pair mechanism.
Asunto(s)
Pájaros Cantores , Taxia , Animales , Pájaros Cantores/metabolismo , Procesos Fotoquímicos , Migración Animal , Campos Magnéticos , Criptocromos/metabolismoRESUMEN
The hydroxyl radical (OH) fuels atmospheric chemical cycling as the main sink for methane and a driver of the formation and loss of many air pollutants, but direct OH observations are sparse. We develop and evaluate an observation-based proxy for short-term, spatial variations in OH (ProxyOH) in the remote marine troposphere using comprehensive measurements from the NASA Atmospheric Tomography (ATom) airborne campaign. ProxyOH is a reduced form of the OH steady-state equation representing the dominant OH production and loss pathways in the remote marine troposphere, according to box model simulations of OH constrained with ATom observations. ProxyOH comprises only eight variables that are generally observed by routine ground- or satellite-based instruments. ProxyOH scales linearly with in situ [OH] spatial variations along the ATom flight tracks (median r2 = 0.90, interquartile range = 0.80 to 0.94 across 2-km altitude by 20° latitudinal regions). We deconstruct spatial variations in ProxyOH as a first-order approximation of the sensitivity of OH variations to individual terms. Two terms modulate within-region ProxyOH variations-water vapor (H2O) and, to a lesser extent, nitric oxide (NO). This implies that a limited set of observations could offer an avenue for observation-based mapping of OH spatial variations over much of the remote marine troposphere. Both H2O and NO are expected to change with climate, while NO also varies strongly with human activities. We also illustrate the utility of ProxyOH as a process-based approach for evaluating intermodel differences in remote marine tropospheric OH.