Apparent Turnover Research Articles

The Wall Teichoic Acid Polymerase TagF Is Non-processive in Vitro and Amenable to Study Using Steady State Kinetic Analysis

Wall teichoic acids are a chemically diverse group of anionic polymers that constitute up to 50% of the Gram-positive cell wall. These polymers play a pivotal role in virulence and have been implicated in a diverse range of physiological functions. The TagF-like family of enzymes has been shown to be responsible for wall teichoic acid priming and polymerization events. Although many such enzymes are well validated therapeutic targets, a mechanistic understanding of this enzyme family has remained elusive. TagF is the prototypical teichoic acid polymerase and uses CDP-glycerol to catalyze synthesis of the linear (1,3)-linked poly(glycerol phosphate) teichoic acid in Bacillus subtilis 168. Here we used a synthetic soluble analog of the natural substrate of the enzyme, Lipid , to conduct the first detailed mechanistic investigation of teichoic acid polymerization. Through the use of a new high pressure liquid chromatography-based assay to monitor single glycerol phosphate incorporations into the Lipid analog, we conducted a detailed analysis of reaction product formation patterns and unequivocally showed TagF to be non-processive in vitro. Furthermore by monitoring the kinetics of polymerization, we showed that Lipid analog species varying in size have the same K(m) value of 2.6 microm and validated use of Bi Bi velocity expressions to model the TagF enzyme system. Initial rate analysis showed that TagF catalyzes a sequential Bi Bi mechanism where both substrates are added to the enzyme prior to product release consistent with a single displacement chemical mechanism.

Study of the selective catalytic reduction of NOx on an efficient Fe/HBEA zeolite catalyst for heavy duty diesel engines

The present paper addresses the removal of NOx from the exhaust of heavy duty vehicles using the SCR technique. The studies were conducted with a highly active H-BEA zeolite exhibiting a molar Si/Al ratio of 12.5 and a Fe load of 1.0wt.% (1Fe/HBEA). The pronounced efficiency of 1Fe/HBEA is reflected by the apparent turnover frequency being superior to traditional V2O5/WO3/TiO2. The nature of the Fe sites was investigated with high resolution transmission electron microscopy (HRTEM), 57Fe Mössbauer spectroscopy and powder X-ray diffraction (PXRD). In connection with previous examinations it is deduced that the iron sites represent octahedrally coordinated high spin Fe3+ cations. Furthermore, highly dispersed species, which are the most active sites, are supposed to be paramagnetic, while oligomeric and particulate structures indicate superparamagnetic behaviour.The practical evaluation of the 1Fe/HBEA catalyst was systematically carried out including laboratory studies of granulated powder and honeycomb samples as well as engine bench tests. For the latter studies a coated honeycomb prototype was employed showing very similar efficiency as referred to a commercial V2O5/WO3/TiO2 pattern.Furthermore, 1Fe/HBEA exhibits pronounced hydrothermal stability after aging at 550°C which represents an elevated exhaust temperature of heavy duty vehicles. The aging caused no change in fast SCR, i.e. when a c(NO2)/c(NOx) ratio of 0.5 was used, and only minor decline in standard SCR. The slight aging effect is mainly referred to little decrease in BET surface area and NH3 uptake, respectively. PXRD indicated maintenance of the BEA structure, whereas 27Al nuclear magnetic resonance spectroscopy showed removal of some Al from the zeolite framework. Contrary, UV–vis spectroscopy evidenced no effect of hydrothermal aging on the composition of the Fe sites. Finally, the catalyst also maintained its efficiency after SO2 aging at 300°C. Diffuse reflectance infrared Fourier transform spectroscopic studies showed adsorption of molecular SO2 on the zeolite substrate releasing already at about 400°C.

The Gcn5 Bromodomain of the SAGA Complex Facilitates Cooperative and Cross-tail Acetylation of Nucleosomes

Bromodomains are acetyl lysine binding modules found in many complexes that regulate gene transcription. In budding yeast, the coactivator complex SAGA (Spt-Ada-Gcn5-acetyl-transferase) predominantly facilitates transcription of stress-activated genes and requires the bromodomain of the Gcn5 subunit for full activation of a number of these genes. This bromodomain has previously been shown to promote retention of the complex to H3 and H4 acetylated nucleosomes. Because the SAGA complex mediates histone H3 acetylation, we sought to determine to what extent the Gcn5 bromodomain directly modulates histone acetylation activity. Kinetic analysis of SAGA-mediated acetylation of nucleosomal substrates reveals that this bromodomain: 1) is required for the cooperative acetylation of nucleosomes, 2) enhances acetylation of an H3 histone tail when the other H3 tail within a nucleosome is already acetylated, and 3) augments the acetylation turnover of nucleosomes previously acetylated at lysine 16 of the histone H4 tails. These results indicate that the Gcn5 bromodomain promotes the establishment of nucleosome acetylation through multiple mechanisms and more generally show how chromatin recognition domains can modulate the enzymatic activity of chromatin modifying complexes.

Active-Site Motions and Polarity Enhance Catalytic Turnover of Hydrated Subtilisin Dissolved in Organic Solvents

The enzyme subtilisin Carlsberg was surfactant-solubilized into two organic solvents, isooctane and tetrahydrofuran, and hydrated through stepwise changes in the thermodynamic water activity, a(w). The apparent turnover number k(cat)(app) in these systems ranged from 0.2 to 80 s(-1) and increased 11-fold in isooctane and up to 50-fold in tetrahydrofuran with increasing a(w). (19)F NMR relaxation experiments employing an active-site inhibitor were used to assess the dependence of active-site motions on a(w). The rates of NMR-derived fast (k > 10(7) s(-1)) and slow (k < 10(4) s(-1)) active-site motions increased in both solvents upon hydration, but only the slow motions correlated with k(cat). The (19)F chemical shift was a sensitive probe of the local electronic environment and provided an empirical measure of the active-site dielectric constant epsilon(as), which increased with hydration to epsilon(as) approximately 13 in each solvent. In both solvents, the transition state free energy data and epsilon(as) followed Kirkwood's model for the continuum solvation of a dipole, indicating that water also enhanced catalysis by altering the active-site's electronic environment and increasing its polarity to better stabilize the transition state. These results reveal that favorable dynamic and electrostatic effects both contribute to accelerated catalysis by solubilized subtilisin Carlsberg upon hydration in organic solvents.

Identification of the oxygen activation site in monomeric sarcosine oxidase: role of Lys265 in catalysis.

Monomeric sarcosine oxidase (MSOX) catalyzes the oxidation of N-methylglycine and contains covalently bound FAD that is hydrogen bonded at position N(5) to Lys265 via a bridging water. Lys265 is absent in the homologous but oxygen-unreactive FAD site in heterotetrameric sarcosine oxidase. Isolated preparations of Lys265 mutants contain little or no flavin but can be covalently reconstituted with FAD. Mutation of Lys265 to a neutral residue (Ala, Gln, Met) causes a 6000- to 9000-fold decrease in apparent turnover rate whereas a 170-fold decrease is found with Lys265Arg. Substitution of Lys265 with Met or Arg causes only a modest decrease in the rate of sarcosine oxidation (9.0- or 3.8-fold, respectively), as judged by reductive half-reaction studies which show that the reactions proceed via an initial enzyme.sarcosine charge transfer complex and a novel spectral intermediate not detected with wild-type MSOX. Oxidation of reduced wild-type MSOX (k = 2.83 x 10(5) M(-1) s(-1)) is more than 1000-fold faster than observed for the reaction of oxygen with free reduced flavin. Mutation of Lys265 to a neutral residue causes a dramatic 8000-fold decrease in oxygen reactivity whereas a 250-fold decrease is observed with Lys265Arg. The results provide definitive evidence for Lys265 as the site of oxygen activation and show that a single positively charged amino acid residue is entirely responsible for the rate acceleration observed with wild-type enzyme. Significantly, the active sites for sarcosine oxidation and oxygen reduction are located on opposite faces of the flavin ring.

Cell–Cell Contact: Cooperating Clusters of Actin and Cadherin

Cooperation between cadherins and actin critically influences tissue organization. A new report identifies distinct pools of actin filaments that influence the spatial distribution of cadherins at cell-cell contacts.

HSTACS Imaging of M82: A Comparison of Mass and Size Distribution Functions of the Younger Nuclear and Older Disk Clusters

We present the results obtained from an objective search for stellar clusters, both in the currently active nuclear starburst region, and in the post-starburst disk of M82. Images obtained with the HST/ACS in F435W(B), F555W(V), and F814W(I) filters were used in the search for the clusters. We detected 653 clusters of which 393 are located outside the central 450 pc in the post-starburst disk of M82. The luminosity function of the detected clusters show an apparent turnover at B=22 mag (M_B=-5.8), which we interpret from Monte Carlo simulations as due to incompleteness in the detection of faint clusters, rather than an intrinsic log-normal distribution. We derived a photometric mass of every detected cluster from models of simple stellar populations assuming a mean age of either an 8 (nuclear clusters) or 100 (disk clusters) million years old. The mass functions of the disk (older) and the nuclear (younger) clusters follow power-laws, the former being marginally flatter (alpha=1.5+/-0.1) than the latter (alpha=1.8+/-0.1). The distribution of sizes (Full Width at Half Maximum) of clusters brighter than the apparent turn-over magnitude (mass>2E+4 Mo) can be described by a log-normal function. This function peaks at 10 pc for clusters more massive than 1E+5 Mo, whereas for lower masses, the peak is marginally shifted to larger values for the younger, and smaller values for the older clusters. The observed trend towards flattening of the mass function with age, together with an over-abundance of older compact clusters, imply that cluster disruption in M82 is both dependent on the mass and size of the clusters.

Light‐Driven Biocatalytic Oxidation and Reduction Reactions: Scope and Limitations

The quest for practical regeneration concepts for nicotinamide-dependent oxidoreductases continues. Recently we proposed the use of visible light to promote the direct reductive regeneration of a flavin-dependent monooxygenase. With this enzyme (PAMO-P3) light-driven enantioselective Baeyer-Villiger oxidations were performed. In spite of the significant reduction in the complexity achieved, catalytic performance of the novel approach did not meet the requirements for an efficient biocatalytic oxygenation system. Driven by this ultimate goal, we further investigated the limiting factors of our particular system. We discovered that oxidative uncoupling of the flavin-regeneration reaction from enzymatic O2-activation accounts for the futile consumption of approximately 95% of the reducing equivalents provided by the sacrificial electron donor, EDTA. Furthermore, it was found that the apparent turnover frequency (TOF) for PAMO-P3 in the present setup is approximately two orders of magnitude lower than in conventional setups that use NADPH as reductant. This finding was traced to sluggish electron transfer kinetics that arose from an impeded interaction between PAMO-P3-bound FAD and the reducing catalyst. The limiting factors and potential approaches for their circumvention are discussed. Furthermore, we broadened the light-driven regeneration approach to the class of flavin-dependent reductases. By using the Old Yellow Enzyme homologue YqjM as a model system, a significantly higher catalytic turnover for the enzyme catalyst was achieved, which we assign to a higher accessibility of the prosthetic group as well as to the absence of oxidative uncoupling.

Molecular modelling and experimental studies on steam gasification of low-rank coals catalysed by iron species

Pyrolysis and catalytic steam gasification of brown coal containing iron hydroxyl complexes have been investigated experimentally and with semi-empirical and density functional theory molecular modelling. Pyrolysis yielded mainly CO2, CO, and reduced iron species. Catalytic steam gasification at 900 °C after 15 min, consumed 20 wt.% additional char and a higher than expected yield of H2 due to post-gasification reactions; inorganic and organic oxygen in char increased compared to pyrolysis. Apparent turnover numbers for catalytic gasification were 12–22 mole of carbon per mole of iron. The distribution of iron species in brown coal indicated small iron clusters are likely to form on heating; pyrolysis was thus modelled using molecules of char with [Fe3], [Fe5] and [Fe3O], and the active site for gasification was shown to be [Fe–C]. The mechanism of catalytic gasification involved H2O chemi-adsorbed on [Fe–C], formation of the [Fe ← OH2] coordination bond, with H2 produced via iron hydride complexes. Formation of CO was via oxygen insertion into [Fe–C] to form [Fe–O–C] that decomposed into CO and another [Fe–C] site. Lower activation barriers were obtained for concerted chemistry involving iron-hydrides. Active sites in char were accessible to H2O as pores had developed around iron species; large sized iron species were not catalytically active but caused large pores to form in char.

Population Pharmacodynamic Modelling of Aspirin- and Ibuprofen-Induced Inhibition of Platelet Aggregation in Healthy Subjects

The objective of this study was to develop a mechanism-based pharmacodynamic model that characterizes the antiplatelet effects of aspirin (acetylsalicylic acid) and ibuprofen alone and in combination. Ten healthy volunteers were enrolled in a single-blinded, randomized, three-way crossover study. Treatments consisted of single doses of oral aspirin (325 mg) and ibuprofen (400 mg) and concomitant administration of aspirin (325 mg) and ibuprofen (400 mg). Ex vivo whole blood platelet aggregation induced by collagen (1 microg/mL) or arachidonic acid (0.5 mmol/L) was measured by impedance aggregometry. Model development and population parameter estimation were performed using nonlinear mixed-effects modelling implemented in NONMEM. Relatively complete inhibition of platelet aggregation was achieved following aspirin treatment (approximately 77% inhibition within 2 hours), and return to baseline values occurred within 72-96 hours after dosing. In contrast, treatment with ibuprofen alone or in combination with aspirin produced transient inhibition of platelet aggregation, with complete recovery observed in 6-8 hours. The final pharmacodynamic model was based on the turnover of cyclo-oxygenase-1 (COX-1) enzyme, and incorporated irreversible inhibition by aspirin and reversible binding and antiplatelet effects of ibuprofen. The temporal response profiles from all three study arms were well described by the final model, and the parameters were estimated with good precision. The apparent turnover rate constant for COX-1 (kout) and the irreversible inhibition rate constant for aspirin (K) were estimated to be 0.0209 h(-1) and 0.152 (mg/L)(-1).h(-1), with interindividual variability of 30.6% and 26.2%, respectively. Simulations were used to evaluate the influence of clinically relevant ibuprofen regimens on the antiplatelet effect of aspirin, confirming clinical reports that the antiplatelet effect of aspirin would be blocked when multiple daily doses of ibuprofen are given, even if taken after aspirin administration. A mechanism-based pharmacodynamic model has been developed that characterizes the antiplatelet effects of aspirin and ibuprofen, alone and concomitantly, and predicts a significant inhibition of aspirin antiplatelet effects in the presence of a typical ibuprofen dosing regimen.

Chaperone function in organic co-solvents: Experimental characterization and modeling of a hyperthermophilic chaperone subunit from Methanocaldococcus jannaschii

Molecular chaperones play a central role in maintaining protein structure within a cell. Previously, we determined that the gene encoding a molecular chaperone, a thermosome, from the hyperthermophilic archaeon Methanocaldococcus jannaschii is upregulated upon lethal heat shock. We have recombinantly expressed this thermosome (rTHS) and show here that it is both stable and fully functional in aqueous solutions containing water-miscible organic co-solvents. Based on circular dichroism the secondary structure of rTHS was not affected by one-hour exposures to a variety of co-solvents including 30% v/v acetonitrile (ACN) and 50% methanol (MeOH). By contrast, the secondary structure of a mesophilic homologue, GroEL/GroES (GroE), was substantially disrupted. rTHS reduced the aggregation of ovalbumin and citrate synthase in 30% ACN, assisted refolding of citrate synthase upon solvent-inactivation, and stabilized citrate synthase and glutamate dehydrogenase in the direct presence of co-solvents. Apparent total turnover numbers of these enzymes in denaturing solutions increased by up to 2.5-fold in the presence of rTHS. Mechanistic models are proposed to help ascertain specific conditions that could enhance or limit organic solvent-induced chaperone activity. These models suggest that thermodynamic stability and the reversibility of enzyme unfolding play key roles in the effectiveness of enzyme recovery by rTHS.

Lemurs

Lemurs

Intensification of the solvent-free catalytic hydroformylation of cyclododecatriene: Comparison of a stirred batch reactor and a heat-exchange reactor

The potential of heat-exchange reactors with mm-scale channels to provide process intensification for homogeneously catalysed gas–liquid reactions was explored. The solvent-free hydroformylation of cyclododecatriene using a homogeneous catalyst was carried out in a heat-exchange (HEx) reactor with mm-scale thin channels, and in a stirred batch autoclave for comparative purposes. The reaction was carried out using generally a concentration of 0.3 mol% catalyst from 50–85 °C temperatures and between 12 and 40 bar pressure. This channel flow is expected to provide increases in mass transfer while high heat transfer capability will accommodate the increased heat transfer duty resulting from increased reaction rates and the absence of the solvent. A simple kinetic model of the data obtained using both reactor types is derived allowing a comparison based on apparent turn-over frequencies. Operation in the HEx reactor was free of mass transfer limitations and the observed turnover frequency was independent of catalyst concentration. By contrast the catalyst productivity in the autoclave was a function of its concentration indicating mass transfer limitations. The observed reaction rate, in terms of apparent turnover frequency was 10–15 times higher in the heat-exchange reactor than the laboratory scale stirred tank. The selectivity to the desired monoaldehyde product was also higher in the HEx reactor. The temperature, pressure and catalyst concentration appear to have little influence of reaction selectivity (for the monoaldehyde) and the product distribution, this being dependent only on the concentration of cyclododecatriene and monoaldehyde. The reasons for this behaviour are discussed in detail.

Lignin is preserved in the fine silt fraction of an arable Luvisol

Knowledge about the fate of individual biomolecules during the decomposition process in soil is limited. We used the natural isotopic label introduced by 23 years of continuous maize cropping, together with compound specific 13C isotope analysis, to study lignin monomers in particle size fractions of a Luvisol. Isotope data indicated apparent decadal turnover times for lignin. A kinetic model suggests the existence of a fast and a slow decomposing lignin pool in the soil, reconciling a low stock-to-input ratio with decadal turnover times. We found new, maize-derived lignin primarily in the 63–2000 μm fraction, whereas old, C 3-derived lignin from the pre-maize vegetation had accumulated mainly in the silt (2–20 μm) fraction. This distribution of lignin differed from that of total organic carbon, which was concentrated in the <2 μm fraction. Old, C 3-derived carbon in all the soil fractions was depleted in lignin compared to new, maize-derived carbon. The observation that the 2–20 μm fraction was less depleted than the others indicates that lignin preservation is particle size specific, but the underlying mechanism controlling its preservation is not clear.

Status of Tern Colonies in the Honduras Bay Islands

In the first comprehensive survey of tern colonies in the Honduras Bay Islands, 46 cays were surveyed in 2005 and 2006 and three species of terns were observed nesting in colonies on ten individual cays. Apparent colony turnover was high between years for Least (Sternula antillarum) and Roseate (Sterna dougallii) Terns, from 71% to 100%, respectively. The first nest records of Bridled Tern (Onychoprion anaethetus) for Honduras are documented.

Tetrapod Footprint Biostratigraphy and Biochronology

Tetrapod footprints have a fossil record in rocks of Devonian-Neogene age. Three principal factors limit their use in biostratigraphy and biochronology (palichnostratigraphy): invalid ichnotaxa based on extramorphological variants, slow apparent evolutionary turnover rates and facies restrictions. The ichnotaxonomy of tetrapod footprints has generally been oversplit, largely due to a failure to appreciate extramorphological variation. Thus, many tetrapod footprint ichnogenera and most ichnospecies are useless phantom taxa that confound biostratigraphic correlation and biochronological subdivision. Tracks rarely allow identification of a genus or species known from the body fossil record. Indeed, almost all tetrapod footprint ichnogenera are equivalent to a family or a higher taxon (order, superorder, etc.) based on body fossils. This means that ichnogenera necessarily have much longer temporal ranges and therefore slower apparent evolutionary turnover rates than do body fossil genera. Because of this, footprints cannot provide as refined a subdivision of geological time as do body fossils. The tetrapod footprint record is much more facies controlled than the tetrapod body fossil record. The relatively narrow facies window for track preservation, and the fact that tracks are almost never transported, redeposited or reworked, limits the facies that can be correlated with any track-based biostratigraphy. A Devonian-Neogene global biochronology based on tetrapod footprints generally resolves geologic time about 20 to 50 percent as well as does the tetrapod body fossil record. The following globally recognizable time intervals can be based on the track record: (1) Late Devonian; (2) Mississippian; (3) Early-Middle Pennsylvanian; (4) Late Pennsylvanian; (5) Early Permian; (6) Late Permian; (7) Early-Middle Triassic; (8) late Middle Triassic; (9) Late Triassic; (10) Early Jurassic; (11) Middle-Late Jurassic; (12) Early Cretaceous; (13) Late Cretaceous; (14) Paleogene; (15) Neogene. Tetrapod footprints are most valuable in establishing biostratigraphic datum points, and this is their primary value to understanding the stratigraphic (temporal) dimension of tetrapod evolution.

Lobeline Attenuates Methamphetamine-induced Stereotypy in Adolescent Mice

In this study, we investigated the effects of lobeline, an alkaloid constituent of Indian tobacco, on methamphetamine (METH)-induced stereotypy in male ICR mice (41-50 days old), an animal model for amphetamine psychosis. After a single administration of METH (10 mg/kg, i.p.), mice showed an initial short-lasting hyperlocomotion and subsequent stereotyped behaviors with a plateau level 25 min after drug challenge. Pretreatment with lobeline (3.0-30 mg/kg, i.p.) 15 min prior to the drug challenge significantly decreased the intensity of stereotypy and increased its latency to onset in a dose-dependent manner, especially 20 min after the drug challenge. In saline challenge groups, the doses of lobeline examined did not affect spontaneous locomotion nor induced any stereotyped behaviors. High-performance liquid chromatography analysis revealed that the range of lobeline doses examined except 30 mg/kg did not affect apparent monoamine turnover in the cerebral cortex, the region of the striatum and nucleus accumbens, and the region of the thalamus and hypothalamus of the mice 20 and 60 min after the drug challenge. These results suggested that the inhibitory effect of lobeline (3.0-10 mg/kg) on METH-induced stereotypy was not attributed to the change in the apparent monoamine turnover.

Characterization and Activity Analysis of Catalytic Water Oxidation Induced by Hybridization of [(OH2)(terpy)Mn(μ-O)2Mn(terpy)(OH2)]3+ and Clay Compounds

Hybridization of [(OH(2))(terpy)Mn(mu-O)(2)Mn(terpy)(OH(2))](3+) (terpy= 2,2':6',2' '-terpyridine) (1) and mica clay yielded catalytic dioxygen (O(2)) evolution from water using a CeIV oxidant. The reaction was characterized by various spectroscopic measurements and a kinetic analysis of O(2) evolution. X-ray diffraction (XRD) data indicates the interlayer separation of mica changes upon intercalation of 1. The UV-vis diffuse reflectance (RD) and Mn K-edge X-ray absorption near-edge structure (XANES) data suggest that the oxidation state of the di-mu-oxo Mn(2) core is Mn(III)-Mn(IV), but it is not intact. In aqueous solution, the reaction of 1 with a large excess Ce(IV) oxidant led to decomposition of 1 to form MnO(4-) ion without O(2) evolution, most possibly by its disproportionation. However, MnO(4-) formation is suppressed by adsorption of 1 on clay. The maximum turnover number for O(2) evolution catalyzed by 1 adsorbed on mica and kaolin was 15 and 17, respectively, under the optimum conditions. The catalysis occurs in the interlayer space of mica or on the surface of kaolin, whereas MnO(4-) formation occurs in the liquid phase, involving local adsorption equilibria of adsorbed 1 at the interface between the clay surface and the liquid phase. The analysis of O(2) evolution activity showed that the catalysis requires cooperation of two equivalents of 1 adsorbed on clay. The second-order rate constant based on the concentration (mol g(-1)) of 1 per unit weight of clay was 2.7 +/- 0.1 mol(-1) s(-1) g for mica, which is appreciably lower than that for kaolin (23.9 +/- 0.4 mol(-1) s(-1) g). This difference can be explained by the localized adsorption of 1 on the surface for kaolin. However, the apparent turnover frequency ((kO(2))app/s(-1)) of 1 on mica was 2.2 times greater than on kaolin when the same fractional loading is compared. The higher cation exchange capacity (CEC) of mica statistically affords a shorter distance between the anionic sites to which 1 is attracted electrostatically, making the cooperative interaction between adsorbed molecules of 1 easier than that on kaolin. The higher CEC is important not only for attaining a higher loading but also for the higher catalytic activity of adsorbed 1.

Lignin turnover in arable soil and grassland analysed with two different labelling approaches

SummaryWhen modelling the carbon dynamics of temperate soils, soil organic carbon (SOC) is often represented by three kinetic pools, i.e. fast, slow and passive/inert. Lignin is often considered to be relatively resistant to decomposition, thus possibly contributing to the passive SOC pool. One way to assess SOC turnover under natural conditions is to follow the fate of 13C‐labelled biomass in soils. We used compound‐specific isotope analysis to analyse CuO oxidation products of lignin from grassland topsoils and from an arable topsoil that had received a natural (by C3‐C4 vegetation change) or an artificial (by fumigation with labelled CO2) isotopic label for 9–23 years. Results indicate faster apparent turnover for lignin (5–26 years in grassland, 9–38 years in arable soil) compared with bulk SOC (20–26 years in grassland, 51 years in arable soil). Although these calculated lignin turnover times cannot be extrapolated to the whole soil profiles, this paper provides isotopic evidence that lignin in soils is not preferentially preserved, which is a consistent result from both ways of isotopic labelling. It also demonstrates, however, that a considerable proportion of lignin in temperate soils can be stabilized for at least a few decades.

Methamphetamine Reward in Mice as Assessed by Conditioned Place Preference Test with Supermex® Sensors: Effect of Subchronic Clorgyline Pretreatment

Recent studies in our laboratory have shown that methamphetamine (METH)-induced hyperlocomotion and behavioral sensitization in mice were inhibited by clorgyline, an irreversible monoamine oxidase inhibitor. In this study, the effect of clorgyline pretreatment on METH-induced rewarding effect was assessed by a conditioned place preference (CPP) test, using an apparatus developed with Supermex sensors (infrared pyroelectric sensors). Although intact male ICR mice showed significant CPP for METH (0.5 mg/kg, i.p.), pretreatment with subchronic clorgyline (0.1 and 10 mg/kg, s.c.) did not affect the magnitude of CPP. At a dose of 1 mg/kg, pretreatment of the mice with clorgyline showed a similar CPP index in both saline/saline and METH/saline pairing groups. During the conditioning session, the mice did not express behavioral sensitization to METH. Pretreatment with clorgyline (0.1, 1, and 10 mg/kg) decreased striatal apparent monoamine turnover in a dose-dependent manner. These results indicated that clorgyline pretreatment (0.1 and 10 mg/kg) did not influence the METH-induced rewarding effect in mice, although pretreatment of the mice with clorgyline at a dose of 1 mg/kg appeared to influence the CPP for METH.