Spatial variation in flux, δ<Superscript>13</Superscript>C and δ<Superscript>2</Superscript>H of methane in a small Arctic lake with fringing wetland in western Greenland

Small lakes in northern latitudes represent a significant source of CH₄ to the atmosphere that is predicted to increase with warming in the Arctic. Yet, whole-lake CH₄ budgets are lacking as are measurements of δ¹³C-CH₄ and δ²H-CH₄. In this study, we quantify spatial variability of diffusive and ebullitive fluxes of CH₄ and corresponding δ¹³C-CH₄ and δ²H-CH₄ in a small, Arctic lake system with fringing wetland in southwestern Greenland during summer. Net CH₄ flux was highly variable, ranging from an average flux of 7 mg CH₄ m^?2 d^?1 in the deep-water zone to 154 mg CH₄ m^?2 d^?1 along the lake margin. Diffusive flux accounted for ~8.5 % of mean net CH₄ flux, with plant-mediated and ebullitive flux accounting for the balance of the total net flux. Methane content of emitted ebullition was low (mean ± SD 10 ± 17 %) compared to previous studies from boreal lakes and wetlands. Isotopic composition of net CH₄ emissions varied widely throughout the system, with δ¹³C-CH₄ ranging from ?66.2 to ?55.5 ‰, and δ²H-CH₄ ranging from ?345 to ?258 ‰. Carbon isotope composition of CH₄ in ebullitive flux showed wider variation compared to net flux, ranging from ?69.2 to ?49.2 ‰. Dissolved CH₄ concentrations were highest in the sediment and decreased up the water column. Higher concentrations of CH₄ in the hypoxic deep water coincided with decreasing dissolved O₂ concentrations, while methanotrophic oxidation dominated in the epilimnion based upon decreasing concentrations and increasing values of δ¹³C-CH₄ and δ²H-CH₄. The most depleted ¹³C- and ²H-isotopic values were observed in profundal bottom waters and in subsurface profundal sediments. Based upon paired δ¹³C and δ²H observations of CH₄, acetate fermentation was likely the dominant production pathway throughout the system. However, isotopic ratios of CH₄ in deeper sediments were consistent with mixing/transition between CH₄ production pathways, indicating a higher contribution of the CO₂ reduction pathway. The large spatial variability in fluxes of CH₄ and in isotopic composition of CH₄ throughout a single lake system indicates that the underlying mechanisms controlling CH₄ cycling (production, consumption and transport) are spatially heterogeneous. Net flux along the lake margin dominated whole-lake flux, suggesting the nearshore littoral area dominates CH₄ emissions in these systems. Future studies of whole-lake CH₄ budgets should consider this significant spatial heterogeneity.     

Backbone and Ile-δ1, Leu,Val methyl <Superscript>1</Superscript>H, <Superscript>15</Superscript>N,and <Superscript>13</Superscript>C,chemical shift assignments for <Emphasis Type="Italic">Rhizopus chinensis</Emphasis> lipase

Lipase r27RCL is a 296-residue, 33 kDa monomeric enzyme with high ester hydrolysis activity, which has significant applications in the baking, paper and leather industries. The lipase gene proRCL from Rhizopus microsporus var. chinensis (also Rhizopus chinensis) CCTCC M201021 was cloned as a fusion construct C-terminal to a maltose-binding protein (MBP) tag, and expressed as MBP-proRCL in an Escherichia coli BL21 trxB (DE3) expression system with uniform ²H,¹³C,¹⁵N-enrichment and Ile-δ1, Leu, and Val ¹³CH₃ methyl labeling. The fusion protein was hydrolyzed by Kex2 protease at the recognition site Lys-Arg between residues ?29 and ?28 of the prosequence, producing the enzyme form called r27RCL. Here we report extensive backbone ¹H, ¹⁵N, and ¹³C, as well as Ile-δ1, Leu, and Val side chain methyl, NMR resonance assignments for r27RCL.     

Metal–metal bonding and aromaticity in [M<Subscript>2</Subscript>(NHCHNH)<Subscript>3</Subscript>]<Subscript>2</Subscript> (μ-E)<Subscript>2</Subscript> (E = O,S; M = Nb,Mo, Tc,Ru, Rh)

The nature of M–M bonding and aromaticity of [M₂(NHCHNH)₃]₂(μ-E)₂ (E?=?O, S; M?=?Nb, Mo, Tc, Ru, Rh) was investigated using atoms in molecules (AIM) theory, electron localization function (ELF), natural bond orbital (NBO) and molecular orbital analysis. These analyses led to the following main conclusions: in [M₂(NHCHNH)₃]₂(μ-E)₂ (E?=?O, S; M?=?Nb, Mo, Tc, Ru, Rh), the Nb–Nb, Ru–Ru, and Rh–Rh bonds belong to “metallic” bonds, whereas Mo–Mo and Tc–Tc drifted toward the “dative” side; all these bonds are partially covalent in character. The Nb–Nb, Mo–Mo, and Tc–Tc bonds are stronger than Ru–Ru and Rh–Rh bonds. The M–M bonds in [M₂(NHCHNH)₃]₂(μ-S)₂ are stronger than those in [M₂(NHCHNH)₃]₂(μ-O)₂ for M?=?Nb, Mo, Tc, and Ru. The NICS(1)_ZZ values show that all of the studied molecules, except [Ru₂(NHCHNH)₃]₂(μ-O)₂, are aromaticity molecules. O-bridged compounds have more aromaticity than S-bridged compounds.

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Graphical Abstract Left Molecular graph, and right electron localization function (ELF) isosurface of [M₂(NHCHNH)₃]₂(μ-E)₂(E?=?O, S; M?=?Nb, Mo, Tc, Ru, Rh)

     

Improved accuracy in measuring one-bond and two-bond <Superscript>15</Superscript>N,<Superscript>13</Superscript>C<Superscript>α</Superscript> coupling constants in proteins by double-inphase/antiphase (DIPAP) spectroscopy

An extension to HN(CO-α/β-N,C^α-J)-TROSY (Permi and Annila in J Biomol NMR 16:221–227, 2000) is proposed that permits the simultaneous determination of the four coupling constants ¹ J _{N′(i)Cα(i)}, ² J _HN(i)Cα(i), ² J _{Cα(i−1)N′(i)}, and ³ J _{Cα(i−1)HN(i)} in ¹⁵N,¹³C-labeled proteins. Contrasting the original scheme, in which two separate subspectra exhibit the ² J _CαN′ coupling as inphase and antiphase splitting (IPAP), we here record four subspectra that exhibit all combinations of inphase and antiphase splittings possible with respect to both ² J _CαN′ and ¹ J _N′Cα (DIPAP). Complementary sign patterns in the different spectrum constituents overdetermine the coupling constants which can thus be extracted at higher accuracy than is possible with the original experiment. Fully exploiting data redundance, simultaneous 2D lineshape fitting of the E.COSY multiplet tilts in all four subspectra provides all coupling constants at ultimate precision. Cross-correlation and differential-relaxation effects were taken into account in the evaluation procedure. By applying a four-point Fourier transform, the set of spectra is reversibly interconverted between DIPAP and spin-state representations. Methods are exemplified using proteins of various size.     

<Superscript>1</Superscript>H, <Superscript>13</Superscript>C,and <Superscript>15</Superscript>N resonance assignments for the pro-inflammatory cytokine interleukin-36α

Interleukin-36α (IL-36α) is a recently characterised member of the interleukin-1 superfamily. It is involved in the pathogenesis of inflammatory arthritis in one third of psoriasis patients. By binding of IL-36α to its receptor IL-36R via the NF-κB pathway other cytokines involved in inflammatory and apoptotic cascade are activated. The efficacy of complex formation is controlled by N-terminal processing. To obtain a more detailed view on the structure function relationship we performed a heteronuclear multidimensional NMR investigation and here report the ¹H, ¹³C, and ¹⁵N resonance assignments for the backbone and side chain nuclei of the pro-inflammatory cytokine interleukin-36α.     

Variation in leaf and soil δ<Superscript>15</Superscript>N in diverse tree species in a lowland dipterocarp rainforest,Malaysia

Key message

Large variations in leaf δ ¹⁵ N in Bornean tropical rainforest trees may indicate that various tropical species have species-specific strategy for nitrogen uptake under low soil nutrient conditions, including root symbiotic microorganisms such as ectomycorrhiza.

Abstract

Lowland tropical rainforests in Southeast Asia are characterized by high species diversity despite limited soil nutrient conditions. The plant nitrogen isotope ratio (δ¹⁵N) reflects plant uptake of soil nitrogen. We analyzed δ¹⁵N values and nitrogen content (N %) in leaves and roots of 108 woody species with different types of symbiotic microorganisms, of different life forms (emergent, canopy, sub-canopy, understory, and canopy gap species), and from different families in a Bornean lowland dipterocarp forest to gain more insight into the diversity of nitrogen uptake strategy in the rhizosphere. Leaf δ¹⁵N values in the species studied varied largely from ?7.2 to 5.0 ‰, which is comparable to the values of known Asian trees including temperate, sub-tropical, and tropical mountain forests. Leaf δ¹⁵N also varied significantly among both life forms and families, though the phylogenetically independent contrast (PIC) relationships were not statistically significant among life form, family, and symbiotic types. Some families showed specific leaf δ¹⁵N values; Dipterocarpaceae, the dominant family in the canopy layer with symbiotic ectomycorrhiza in Southeast Asia, had small intraspecific variation and higher leaf δ¹⁵N values (0.03 ‰) compared with species exhibiting arbuscular mycorrhiza, whereas several families such as Burseraceae, Euphorbiaceae, and Myrtaceae showed large interspecific variation in leaf δ¹⁵N (e.g., from ?7.2 to 5.0 ‰ in Euphorbiaceae). These variations suggest that tropical species may have family- or species-specific strategy, such as root symbiotic microorganisms, for nitrogen uptake under low-nutrient conditions in tropical rainforests in Southeast Asia.

     

Presence of Ornithine in the Urate-binding α<Subscript>1</Subscript>—<Subscript>2</Subscript>Globulin

THE urate-binding α₁–α₂ globulin has been isolated from human plasma in a highly purified state¹. The protein was purified by DEAE-‘Sephadex’, ammonium sulphate precipitation and semi-preparative Polyacrylamide gel electrophoresis. The urate-binding α₁–α₂ globulin is a rod-shaped glycoprotein, containing 12.1% carbohydrate, with an isoelectric point of 4.6 and a molecular weight of 67,000 ± 4,000. Amino-acid analysis indicated an unknown basic compound which appeared as an extra peak just in front of lysine¹. To identify this compound, high voltage paper electrophoresis has been carried out on a plate electrophoresis apparatus in pyridine-acetate buffer pH 3.5. A spot separated out corresponding to ornithine. Amino-acid analysis on a BC-200 automatic analyser (Bio-Cal Instruments Co., West Germany), with a 54 cm column at 55° C and with 0.35 M sodium citrate buffer, pH 5.28, as elution buffer at a flow-rate of 150 ml./h, showed that ornithine was present. The presence of ornithine in the protein hydrolysate was also verified by gas chromatography/mass spectrometry².     

Estimation of denitrification potential in a karst aquifer using the <Superscript>15</Superscript>N and <Superscript>18</Superscript>O isotopes of NO<Stack><Subscript>3</Subscript><Superscript>−</Superscript></Stack>

A confined aquifer in the Malm Karst of the Franconian Alb, South Germany was investigated in order to understand the role of the vadose zone in denitrifiaction processes. The concentrations of chemical tracers Sr²⁺ and Cl^– and concentrations of stable isotope ¹⁸O were measured in spring water and precipitation during storm events. Based on these measurements a conceptual model for runoff was constructed. The results indicate that pre-event water, already stored in the system at the beginning of the event, flows downslope on vertical and lateral preferential flow paths. Chemical tracers used in a mixing model for hydrograph separation have shown that the pre-event water contribution is up to 30%. Applying this information to a conceptual runoff generation model, the values of ¹⁵N and ¹⁸O in nitrate could be calculated. Field observations showed the occurence of significant microbial denitrification processes above the soil/bedrock interface before nitrate percolates through to the deeper horizon of the vadose zone. The source of nitrate could be determined and denitrification processes were calculated. Assuming that the nitrate reduction follows a Rayleigh process one could approximate a nitrate input concentration of about 170 mg/l and a residual nitrate concentration of only about 15%. The results of the chemical and isotopic tracers postulate fertilizers as nitrate source with some influence of atmospheric nitrate. The combined application of hydrograph separation and determination of isotope values in ¹⁵N and ¹⁸O of nitrate lead to an improved understanding of microbial processes (nitrification, denitrification) in dynamic systems.     

Nitrogen source,concentration, and NH<Subscript>4</Subscript><Superscript>+</Superscript>:NO<Subscript>3</Subscript><Superscript>−</Superscript> ratio influence shoot regeneration and hyperhydricity in tissue cultured <Emphasis Type="Italic">Aloe polyphylla</Emphasis>

We report on the transformation and expression in sugar beet (Beta vulgaris) hairy roots of a Nicotiana alata NaPI gene encoding a serine proteinase inhibitor (PI) that has been shown to effectively reduce the population of a number of insect pests. Using in-gel analysis, two PI protein activities were detected at approximately 24- and/or 28-kDa in hairy roots generated via Agrobacterium rhizogenes-mediated gene transfer. Immunoblot analysis revealed the presence of the expected ~40 kDa precursor, and in some transformants, a ~20 kDa processing intermediate and the mature 6-kDa PIs. In general, processing of the precursor in the clonal lines was reduced or not detected. The reduced efficiency of post-translational processing of the N. alata PI precursor may be attributed to modification and/or altered folding of the recombinant protein or distinct post-translational machinery functioning in sugar beet hairy roots and Nicotiana. Disclaimer: Mention and/or use of a commercial or proprietary product to the exclusion of others does not constitute endorsement by the USDA.     

Flow of Deposited Inorganic N in Two Gleysol-dominated Mountain Catchments Traced with <Superscript>15</Superscript>NO<Subscript>3</Subscript><Superscript>−</Superscript> and <Superscript>15</Superscript>NH<Subscript>4</Subscript><Superscript>+</Superscript>

In two mountain ecosystems at the Alptal research site in central Switzerland, pulses of ¹⁵NO₃ and ¹⁵NH₄ were separately applied to trace deposited inorganic N. One forested and one litter meadow catchment, each approximately 1600 m², were delimited by trenches in the Gleysols. K¹⁵NO₃ was applied weekly or fortnightly over one year with a backpack sprayer, thus labelling the atmospheric nitrate deposition. After the sampling and a one-year break, ¹⁵NH₄Cl was applied as a second one-year pulse, followed by a second sampling campaign. Trees (needles, branches and bole wood), ground vegetation, litter layer and soil (LF, A and B horizon) were sampled at the end of each labelling period. Extractable inorganic N, microbial N, and immobilised soil N were analysed in the LF and A horizons. During the whole labelling period, the runoff water was sampled as well. Most of the added tracer remained in both ecosystems. More NO₃⁻ than NH₄⁺ tracer was retained, especially in the forest. The highest recovery was in the soil, mainly in the organic horizon, and in the ground vegetation, especially in the mosses. Event-based runoff analyses showed an immediate response of ¹⁵NO₃⁻ in runoff, with sharp ¹⁵N peaks corresponding to discharge peaks. NO₃⁻ leaching showed a clear seasonal pattern, being highest in spring during snowmelt. The high capacity of N retention in these ecosystems leads to the assumption that deposited N accumulates in the soil organic matter, causing a progressive decline of its C:N ratio.     

Influence of Copper,Iron, Zinc and Fe<Stack><Subscript>3</Subscript><Superscript>+</Superscript></Stack> Haemoglobin Levels on the Etiopathogenesis of Chronic Calcific Pancreatitis—A Study in Patients with Pancreatitis

Chronic pancreatitis is a serious condition associated with severe abdominal pain, and a significant percentage of patients progresses to irreversible calcification in pancreas. The present study evaluates the degree to which the levels of trace elements, copper, iron, selenium, zinc and haemoglobin-Fe³⁺, in blood, serum and pancreas have any role to play in the calcification process associated with fibrosis in pancreas. Twenty-seven calcific (CCP) and 23 non-calcific chronic pancreatitis (CP) patients and equal number of age- and sex-matched normal volunteers (50) were enrolled in the study. Surgically removed pancreatic tissue and blood samples were analysed for copper, iron, selenium, zinc, protein, collagen and lipid peroxidation products in terms of malondialdehyde, protein carbonyls, glutathione, methemoglobin, methemoglobin reductase and ceruloplasmin activity levels. We could find that the pancreatic tissue levels of copper, iron, protein and collagen contents were significantly elevated in CCP patients when compared to CP patients. Serum levels of copper, free ionic copper and iron were also elevated in CCP patients. The serum and the pancreatic tissue level of zinc and selenium showed a significant decrease in CCP patients. The level of methemoglobin was elevated more significantly with the concomitant decline in the activity of methemoglobin reductase. There was a positive correlation between the pancreatic level of copper and iron with the collagen and protein levels. The results of the present study revealed that the levels of copper and iron, the pro-oxidants and zinc and selenium may influence calcification process in CCP patients. Hypoxia-related tissue injury due to the formation of oxidised haemoglobin may also contribute to the pathogenesis of calcification in pancreas.     

Defects in meiotic recombination delay progression through pachytene in <Emphasis Type="Italic">Tex19.1</Emphasis><Superscript><Emphasis Type="Italic">−/−</Emphasis></Superscript> mouse spermatocytes

Recombination, synapsis, chromosome segregation and gene expression are co-ordinately regulated during meiosis to ensure successful execution of this specialised cell division. Studies with multiple mutant mouse lines have shown that mouse spermatocytes possess quality control checkpoints that eliminate cells with persistent defects in chromosome synapsis. In addition, studies on Trip13^mod/mod mice suggest that pachytene spermatocytes that successfully complete chromosome synapsis can undergo meiotic arrest in response to defects in recombination. Here, we present additional support for a meiotic recombination-dependent checkpoint using a different mutant mouse line, Tex19.1^?/?. The appearance of early recombination foci is delayed in Tex19.1^?/? spermatocytes during leptotene/zygotene, but some Tex19.1^?/? spermatocytes still successfully synapse their chromosomes and we show that these spermatocytes are enriched for early recombination foci. Furthermore, we show that patterns of axis elongation, chromatin modifications and histone H1t expression are also all co-ordinately skewed towards earlier substages of pachytene in these autosomally synapsed Tex19.1^?/? spermatocytes. We also show that this skew towards earlier pachytene substages occurs in the absence of elevated spermatocyte death in the population, that spermatocytes with features of early pachytene are present in late stage Tex19.1^?/? testis tubules and that the delay in histone H1t expression in response to loss of Tex19.1 does not occur in a Spo11 mutant background. Taken together, these data suggest that a recombination-dependent checkpoint may be able to modulate pachytene progression in mouse spermatocytes to accommodate some types of recombination defect.     

Assimilation and nitrification in pelagic waters: insights using dual nitrate stable isotopes (δ<Superscript>15</Superscript>N, δ<Superscript>18</Superscript>O) in a shallow lake

Nitrate dual stable isotopes (δ¹⁵N and δ¹⁸O of NO₃ ^?) have proven to be a powerful technique to elucidate nitrogen (N) cycling pathways in aquatic systems. We applied this technique for the first time in the pelagic zone of a small temperate meso-eutrophic lake to identify the dominant N cycling pathways, and their spatial and temporal variability. We measured the lake NO₃ ^? δ¹⁵N and δ¹⁸O signatures over an annual cycle and compared them to that of the watershed. Both δ¹⁵N and δ¹⁸O of NO₃ ^? in the lake increased during summer relative to the inputs. Relationships between lake NO₃ ^? isotopic composition and concentrations were different across thermal strata with an apparent isotope effect in the epilimnion of ¹⁵ε_epi = 4.6‰ and ¹⁸ε_epi = 10.9‰. We found a strong deviation of the lake NO₃ ^? δ¹⁸O and δ¹⁵N from the expected 1:1 line for assimilation (slope = 1.73) suggesting that nitrification was co-occurring. We estimated that nitrification could support between 5 and 30% of nitrate-based production during the growing season, but was negligible in early spring and fall, and probably more dominant under ice. We showed that the technique is promising to study N processes at the ecosystem scale in shallow lakes, particularly during winter. Our results suggest that recycled NO₃ ^? could support primary productivity and influence phytoplankton composition in the surface waters of small lakes.     

Foliar N application reduces soil NO<Stack><Subscript>3</Subscript><Superscript>−</Superscript></Stack>-N leaching loss in apple orchards

A comparison of the effects of foliar and soil N application was made in field-grown mature fruiting Gala/M9 apple trees (Malus domestica Borkh) in 2001 and 2002 growing seasons under Pacific Northwest growing conditions in southern British Columbia, Canada. The trees, six years old at the start of the experiment, were treated: (1) with 5 g/l urea sprays supplied every two weeks (7 times) from mid May to mid August (total about 50 g N/tree/year), (2) with the same amount of N applied to the soil with the same timing and quantity as for the foliar treatment, and (3) with no N (control). Leaf color (as SPAD readings) and N concentrations (mg/g), and soil NH₄⁺-N and NO₃^–-N were measured periodically throughout the two seasons. Leached NO₃^–-N was monitored monthly via an anion exchange probe from June to October in 2001 and from May to November in 2002. Shoot length was measured in October and N concentration of one-year-old wood and roots was determined in December of each growing s eason. Soil N application significantly increased shoot length relative to control or foliar N application. Leaf color, leaf N, and N concentration of one-year-old wood and roots were similarly increased relative to control by both soil and foliar N application. These treatments also increased fruit yield relative to control. There was no significant difference in yield and fruit quality between soil and foliar N applications. Soil N application increased soil NH₄⁺-N and NO₃^–-N content in the root zone, and also increased the NO₃^– leaching loss below the root zone especially late in the growing season. Our results suggested that tree N status and yield and fruit quality could be maintained by multiple urea sprays during the growing season in apple orchards, and foliar N application will reduce the risk of soil NO₃^–-N leaching.     

Measurement of imino <Superscript>1</Superscript>H–<Superscript>1</Superscript>H residual dipolar couplings in RNA

Imino ¹H–¹⁵N residual dipolar couplings (RDCs) provide additional structural information that complements standard ¹H–¹H NOEs leading to improvements in both the local and global structure of RNAs. Here, we report measurement of imino ¹H–¹H RDCs for the Iron Responsive Element (IRE) RNA and native E. coli tRNA^Val using a BEST-Jcomp-HMQC2 experiment. ¹H–¹H RDCs are observed between the imino protons in G–U wobble base pairs and between imino protons on neighboring base pairs in both RNAs. These imino ¹H–¹H RDCs complement standard ¹H–¹⁵N RDCs because the ¹H–¹H vectors generally point along the helical axis, roughly perpendicular to ¹H–¹⁵N RDCs. The use of longitudinal relaxation enhancement increased the signal-to-noise of the spectra by ~3.5-fold over the standard experiment. The ability to measure imino ¹H–¹H RDCs offers a new restraint, which can be used in NMR domain orientation and structural studies of RNAs. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effects of activation of μ-, κ<Subscript>1</Subscript>-, δ<Subscript>1</Subscript>-, δ<Subscript>2</Subscript>-, and ORL<Subscript>1</Subscript>-receptors on heart resistance to the pathogenic action of delayed ischemia and reperfusion

Different subtypes of opioid receptors (OR) were activated in rats in vivo to study the activation effect on the heart’s resistance to ischemia and reperfusion. It has been established that administration of deltorphin II, a selective δ₂-OR agonist, lowered the infarct size/area at risk index (IS/AAR) by 23%. Naltrexone, naloxone methiodide (an OR inhibitor not penetrating the blood-brain barrier (BBB)), and naltriben (δ₂-antagonist) eliminated the cardioprotective effect of deltorphin II, while BNTX (a δ₁-antagonist) produced no effect on the cardioprotective action of the δ₂-agonist. The infarct-reducing effect of deltorphin II was eliminated by administration of chelerythrine (a protein kinase C (PKC) inhibitor), glibenclamide (a K_ATP-channels inhibitor), and 5-hydroxydecanoate (a mitochondrial K_ATP-channel blocker). Administration of other opioids did not reduce the IS/AAR index. It has been established that all the deltorphins manifest antiarrhythmic potency. Other opioids do not produce any effect on the incidence of arrhythmia occurrences. The antiarrhythmic effect of deltorphin II was eliminated by preliminary administration of naltrexone, naloxone methiodide, and naltriben, but BNTX did not affect the δ₂-agonist’s anti-arrhythmic effect. The preliminary administration of chelerythrine, a PKC inhibitor, eliminated the δ₂ agonist’s antiarrhythmic action. However, glibenclamide and 5-hydroxydecanoate did not alter the antiarrhythmic effect by deltorphin II. Therefore, activation of the peripheral δ₂-ORs reduces the infarct size and prevents the onset of arrhythmias. The antiarrhythmic effect of the δ₂-OR stimulation is mediated by activating PKC and opening the mitochondrial K_ATP-channels. PKC participates in the antiarrhythmic effect of the δ₂-OR activation, but this effect does not depend on the condition of K_ATP-channels.     

<Emphasis Type="Bold">α</Emphasis>,β-Dehydroamino acids in naturally occurring peptides

α,β-Dehydroamino acids are naturally occurring non-coded amino acids, found primarily in peptides. The review focuses on the type of α,β-dehydroamino acids, the structure of dehydropeptides, the source of their origin and bioactivity. Dehydropeptides are isolated primarily from bacteria and less often from fungi, marine invertebrates or even higher plants. They reveal mainly antibiotic, antifungal, antitumour, and phytotoxic activity. More than 60 different structures were classified, which often cover broad families of peptides. 37 different structural units containing the α,β-dehydroamino acid residues were shown including various side chains, Z and E isomers, and main modifications: methylation of peptide bond as well as the introduction of ester group and heterocycle ring. The collected data show the relation between the structure and bioactivity. This allows the activity of compounds, which were not studied in this field, but which belong to a larger peptide family to be predicted. A few examples show that the type of the geometrical isomer of the α,β-dehydroamino acid residue can be important or even crucial for biological activity.     

A simple strategy for <Superscript>13</Superscript>C,<Superscript>1</Superscript>H labeling at the Ile-γ2 methyl position in highly deuterated proteins

A straightforward approach for the production of highly deuterated proteins labeled with ¹³C and ¹H at Ile-γ2 methyl positions is described. The utility of the methodology is illustrated with an application involving the half proteasome (360 kDa). High quality 2D Ile ¹³C^γ2,¹H^γ2 HMQC data sets, exploiting the methyl-TROSY principle, are recorded with excellent sensitivity and resolution, that compare favorably with Ile ¹³C^δ1,¹H^δ1 spectra. This labeling scheme adds to a growing list of different approaches that are significantly impacting the utility of solution NMR spectroscopy in studies of supra-molecular systems.     

Decline in Ecosystem <Emphasis Type="Italic">δ</Emphasis><Superscript>13</Superscript>C and Mid-Successional Nitrogen Loss in a Two-Century Postglacial Chronosequence

Uncertainty about controls on long-term carbon (C) and nitrogen (N) balance, turnover, and isotopic composition currently limits our ability to predict ecosystem response to disturbance and landscape change. We used a two-century, postglacial chronosequence in Glacier Bay, Alaska, to explore the influence of C and N dynamics on soil and leaf stable isotopes. C dynamics were closely linked to soil hydrology, with increasing soil water retention during ecosystem development resulting in a linear decrease in foliar and soil δ¹³C, independent of shifts in vegetation cover and despite constant precipitation across sites. N dynamics responded to interactions among soil development, vegetation type, microbial activity, and topography. Contrary to the predictions of nutrient retention theory, potential nitrification and denitrification were high, relative to inorganic N stocks, from the beginning of the chronosequence, and gaseous and hydrological N losses were highest at mid-successional sites, 140–165 years since deglaciation. Though leaching of dissolved N is considered the predominant pathway of N loss at high latitudes, we found that gaseous N loss was more tightly correlated with δ¹⁵N enrichment. These results suggest that δ¹³C in leaves and soil can depend as much on soil development and associated water availability as on climate and that N availability and export depend on interactions between physical and biological state factors.