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1.
New Phytol ; 195(2): 408-418, 2012 Jul.
Article in English | MEDLINE | ID: mdl-22537052

ABSTRACT

• Peat bogs have accumulated more atmospheric carbon (C) than any other terrestrial ecosystem today. Most of this C is associated with peat moss (Sphagnum) litter. Atmospheric nitrogen (N) deposition can decrease Sphagnum production, compromising the C sequestration capacity of peat bogs. The mechanisms underlying the reduced production are uncertain, necessitating multifactorial experiments. • We investigated whether glasshouse experiments are reliable proxies for field experiments for assessing interactions between N deposition and environment as controls on Sphagnum N concentration and production. We performed a meta-analysis over 115 glasshouse experiments and 107 field experiments. • We found that glasshouse and field experiments gave similar qualitative and quantitative estimates of changes in Sphagnum N concentration in response to N application. However, glasshouse-based estimates of changes in production--even qualitative assessments-- diverged from field experiments owing to a stronger N effect on production response in absence of vascular plants in the glasshouse, and a weaker N effect on production response in presence of vascular plants compared to field experiments. • Thus, although we need glasshouse experiments to study how interacting environmental factors affect the response of Sphagnum to increased N deposition, we need field experiments to properly quantify these effects.


Subject(s)
Ecological and Environmental Phenomena , Nitrogen/pharmacology , Sphagnopsida/drug effects , Sphagnopsida/growth & development , Linear Models , Models, Biological , Plant Shoots/drug effects , Plant Shoots/physiology
2.
New Phytol ; 191(2): 496-507, 2011 Jul.
Article in English | MEDLINE | ID: mdl-21434930

ABSTRACT

Peatlands in the northern hemisphere have accumulated more atmospheric carbon (C) during the Holocene than any other terrestrial ecosystem, making peatlands long-term C sinks of global importance. Projected increases in nitrogen (N) deposition and temperature make future accumulation rates uncertain. Here, we assessed the impact of N deposition on peatland C sequestration potential by investigating the effects of experimental N addition on Sphagnum moss. We employed meta-regressions to the results of 107 field experiments, accounting for sampling dependence in the data. We found that high N loading (comprising N application rate, experiment duration, background N deposition) depressed Sphagnum production relative to untreated controls. The interactive effects of presence of competitive vascular plants and high tissue N concentrations indicated intensified biotic interactions and altered nutrient stochiometry as mechanisms underlying the detrimental N effects. Importantly, a higher summer temperature (mean for July) and increased annual precipitation intensified the negative effects of N. The temperature effect was comparable to an experimental application of almost 4 g N m(-2) yr(-1) for each 1°C increase. Our results indicate that current rates of N deposition in a warmer environment will strongly inhibit C sequestration by Sphagnum-dominated vegetation.


Subject(s)
Carbon Sequestration/physiology , Nitrogen/metabolism , Soil/chemistry , Sphagnopsida/physiology , Bayes Theorem , Climate , Ecosystem , Linear Models , Models, Statistical , Rain , Seasons , Sphagnopsida/growth & development , Temperature , Wetlands
3.
Eur Radiol ; 18(11): 2549-58, 2008 Nov.
Article in English | MEDLINE | ID: mdl-18491103

ABSTRACT

This comparative study of tumour patients and volunteers aimed at differentiating liver parenchyma from neoplastic lesions by using localised (1)H MRS at 3.0 T as an adjunct to MRI. In total 186 single-voxel proton spectra of the liver were acquired at 3.0 T using the body transmit receive coil. Consecutive stacks of breath-hold spectra were acquired in the PRESS technique at a short echo time of 35 ms and a repetition time of 2,000 ms. Processing of the spectra included spectral alignment with the software package SAGE and quantitative processing with LCModel. The resulting metabolite concentrations were presented in arbitrary units relative to the internal water. In general, the spectra showed four main groups of resonances originating from the methyl protons (0.8-1.1 ppm) and methylene protons of the lipids (1.1-1.5 ppm; 2.0-2.2 ppm) as well as the methyl protons of choline-containing compounds (CCC) at 3.2 ppm. Overall, the CCC and lipid values in malignant liver tumours showed no significant differences to liver parenchyma. On average, total lipid measurements in normal liver parenchyma increased with age, while those of the CCC did not show pertinent changes. Significant differences between the contents of CCC in malignant liver tumours and normal liver parenchyma were not observed, because in patients and volunteers normal liver tissue showed a large variability in the content of CCC.


Subject(s)
Algorithms , Biomarkers, Tumor/analysis , Choline/analysis , Liver Neoplasms/diagnosis , Liver Neoplasms/metabolism , Liver/metabolism , Magnetic Resonance Spectroscopy/methods , Adult , Aged , Female , Humans , Male , Middle Aged , Protons , Reproducibility of Results , Sensitivity and Specificity
4.
Radiologe ; 44(12): 1192-6, 2004 Dec.
Article in German | MEDLINE | ID: mdl-15549225

ABSTRACT

Use of whole-body MRI beyond 1.5 Tesla (T) has initiated a renaissance in spectroscopic procedures (MRS). The superior signal-to-noise ratio of clinical 3T tomographs allows reliable acquisition of MR spectra not only in fixed organs but also in targets moved by breathing such as the liver. The following contribution describes the principles of (1)H MRS and our own initial experiences with spectroscopy of the liver and hepatic malignant tumors with 3T whole-body MRI.


Subject(s)
Image Enhancement/methods , Image Interpretation, Computer-Assisted/methods , Imaging, Three-Dimensional/methods , Liver Neoplasms/diagnosis , Liver/pathology , Magnetic Resonance Imaging/methods , Magnetic Resonance Spectroscopy/methods , Humans , Protons
5.
Mycorrhiza ; 12(4): 175-80, 2002 Aug.
Article in English | MEDLINE | ID: mdl-12189471

ABSTRACT

Simultaneous associations among ectotrophic and ericoid mycorrhizal hosts and their mycorrhizal fungi are expected in boreal bogs where ericaceous shrubs and conifers coexist rooted in an organic matrix dominated by Sphagnum mosses. We were thus prompted to examine, in vitro, the abilities of three ericoid mycorrhizal fungi [ Hymenoscyphus ericae, Oidiodendron maius, and Variable White Taxon (VWT)] to associate with Picea mariana (Pinaceae), with both P. mariana and Rhododendron groenlandicum (Ericaceae) simultaneously, and to decompose Sphagnum fuscum. Hymenoscyphus ericae and VWT developed an intracellular association with roots of P. mariana and with roots of R. groenlandicum. Two strains of O. maius did not form typical infection units in R. groenlandicum, nor did they colonize the root cells of P. mariana. Mass losses incurred by sterilized S. fuscum plants inoculated with these three taxa indicated that O. maius could be more efficient as a free-living saprophyte on this material than either H. ericae or VWT and may in part explain why atypical associations with the roots of ericaceous hosts were formed.


Subject(s)
Mycorrhizae/physiology , Picea/microbiology , Plant Roots/microbiology , Rhododendron/microbiology , Ascomycota/physiology , Bryopsida/metabolism , Culture Media
6.
J Org Chem ; 66(13): 4580-4, 2001 Jun 29.
Article in English | MEDLINE | ID: mdl-11421777

ABSTRACT

Dehydrodidemnin B (DDB or aplidine), a potent antitumoral natural product currently in phase II clinical trials, exists as an approximately 1:1 mixture of two slowly interconverting conformations. These are sufficiently long-lived so as to allow their resolution by HPLC. NMR spectroscopy shows that this phenomenon is a consequence of restricted rotation about the Pyr-Pro(8) terminal amide bond of the molecule's side chain. The same technique also indicates that the overall three-dimensional structures of both the cis and trans isomers of DDB are similar despite the conformational change. Molecular dynamics simulations with different implicit and explicit solvent models show that the ensembles of three-dimensional structures produced are indeed similar for both the cis and trans isomers. These studies also show that hydrogen bonding patterns in both isomers are alike and that each one is stabilized by a hydrogen bond between the pyruvyl unit at the terminus of the molecule's side chain and the Thr(6) residue situated at the junction betwen the macrocycle and the molecule's side chain. Nevertheless, each conformational isomer forms this hydrogen bond using a different pyruvyl carbonyl group: CO(2) in the case of the cis isomer and CO(1) in the case of the trans isomer.


Subject(s)
Antineoplastic Agents/chemistry , Depsipeptides , Peptides, Cyclic/chemistry , Computer Simulation , Magnetic Resonance Spectroscopy , Models, Molecular , Molecular Conformation
7.
J Org Chem ; 65(21): 6992-9, 2000 Oct 20.
Article in English | MEDLINE | ID: mdl-11031021

ABSTRACT

We describe a straightforward synthesis of 9-substituted 3-aminooxazolidinopiperidin-2-ones 4. Some derivatives were prepared for use in peptide synthesis as rigidified surrogates of the Ala-Pro dipeptide. Analysis of the amide derivatives 14 by NMR experiments and molecular mechanics/dynamics calculations shows that the major isomer 14a has a stronger propensity than the minor isomer 14b to adopt beta-turn conformations, and the calculations indicate that in water 14a adopts a stable betaII' turn conformation.


Subject(s)
Peptides/chemistry , Piperidines/chemical synthesis , Magnetic Resonance Spectroscopy , Models, Molecular , Molecular Conformation , Molecular Mimicry , Piperidines/chemistry , Protein Structure, Secondary , Stereoisomerism
8.
Life Sci ; 67(4): 457-61, 2000 Jun 16.
Article in English | MEDLINE | ID: mdl-11003055

ABSTRACT

Several experimental findings indicate that the adhesion molecule N-cadherin participates in distinct processes of embryogenesis that spatiotemporarily correlate with high sensitivity to thalidomide. Therefore, we suppose that thalidomide might interfere with N-cadherin-mediated interactions. This hypothesis is supported by protein-ligand docking studies simulating and characterizing the binding of thalidomide to N-cadherin molecules. Thalidomide was found to bind at the N-terminal domain of N-cadherin mimicking a tryptophan residue which is critical for the homodimerization of the adhesion molecule. Based on these results, we suggest that thalidomide might disturb cellular recognition and migration processes in morphogenesis by interaction with N-cadherin.


Subject(s)
Abnormalities, Drug-Induced/etiology , Cadherins/physiology , Teratogens/toxicity , Thalidomide/toxicity , Abnormalities, Drug-Induced/metabolism , Animals , Chick Embryo , Models, Molecular , Molecular Structure , Teratogens/chemistry , Teratogens/metabolism , Thalidomide/chemistry , Thalidomide/metabolism , Tryptophan/chemistry
9.
Biopolymers ; 50(2): 167-84, 1999 Aug.
Article in English | MEDLINE | ID: mdl-10380341

ABSTRACT

The conformation of oligomers of beta-amino acids of the general type Ac-[beta-Xaa]n-NHMe (beta-Xaa = beta-Ala, beta-Aib, and beta-Abu; n = 1-4) was systematically examined at different levels of ab initio molecular orbital theory (HF/6-31G*, HF/3-21G). The solvent influence was considered employing two quantum-mechanical self-consistent reaction field models. The results show a wide variety of possibilities for the formation of characteristic elements of secondary structure in beta-peptides. Most of them can be derived from the monomer units of blocked beta-peptides with n = 1. The stability and geometries of the beta-peptide structures are considerably influenced by the side-chain positions, by the configurations at the C alpha- and C beta-atoms of the beta-amino acid constituents, and especially by environmental effects. Structure peculiarities of beta-peptides, in particular those of various helix alternatives, are discussed in relation to typical elements of secondary structure in alpha-peptides.


Subject(s)
Amino Acids/chemistry , Oligopeptides/chemistry , Protein Conformation , Diamide , Models, Molecular , Stereoisomerism , Stress, Mechanical
10.
J Med Chem ; 42(10): 1849-54, 1999 May 20.
Article in English | MEDLINE | ID: mdl-10346938

ABSTRACT

A series of substituted 3-amino-5-phenoxythiophenes was synthesized starting from malodinitrile and carbon disulfide. The resulting dicyanoketenedithiolate reacts via Thorpe-Dieckmann cyclization with halogen methanes bearing electron-withdrawing groups to give thiophene-2-thiolates, which can be transformed into 3-amino-5-(methylsulfonyl)thiophene-4-carbonitriles. Replacement of the methylsulfonyl groups by substituted phenolates provides the substituted 3-amino-5-phenoxythiophenes. Some of the derivatives show a considerable inhibitory potency for the L-T3 uptake in inhibition studies on human HepG2 hepatoma cells with maximum values of about 60% at a dose of 10(-5) M for the most potent 2-benzoyl derivatives. The structure of the phenoxythiophenes fits well into a general concept derived for other classes of L-T3 uptake inhibitors, which postulates an angular and perpendicular orientation of the ring systems in these compounds as a prerequisite for an inhibitory potency. Docking studies for the phenoxythiophenes with transthyretin as a receptor model show their preferred attack at the L-T4/L-T3 binding channel.


Subject(s)
Thiophenes/chemical synthesis , Triiodothyronine/antagonists & inhibitors , Humans , Models, Molecular , Molecular Conformation , Structure-Activity Relationship , Thiophenes/chemistry , Thiophenes/pharmacology , Tumor Cells, Cultured
11.
Biochemistry ; 38(19): 6056-62, 1999 May 11.
Article in English | MEDLINE | ID: mdl-10320331

ABSTRACT

Contrary to common protease substrates, the hydrolysis of 4-guanidinophenyl esters of the Boc-Xaa-OGp type by trypsin and trypsin-like proteases performs easily and independently of the structure and chirality of the acyl moiety. The hydrolysis of this new class of substrate mimetics, previously called inverse substrates, is enabled by the highly specific leaving group. However, the mechanism cannot be explained on the basis of the conventional binding model which defines the interactions between the protease and its substrate. Hydrolysis and aminolysis kinetics, protein-ligand docking, and molecular dynamics studies have been carried out in order to get insight into the catalytic mechanism which holds for these substrate mimetics. The experimental and theoretical results obtained for the serine protease trypsin suggest a novel extended kinetic model. It explains the hydrolysis of these types of protease substrates and accounts for the structural consequences for their aminolysis.


Subject(s)
Molecular Mimicry , Trypsin/chemistry , Catalysis , Endopeptidases/chemistry , Endopeptidases/metabolism , Hydrolysis , Models, Molecular , Models, Theoretical , Substrate Specificity , Trypsin/metabolism
12.
Biochemistry ; 37(33): 11434-40, 1998 Aug 18.
Article in English | MEDLINE | ID: mdl-9708978

ABSTRACT

The serine protease trypsin was converted into a site-specific protease which hydrolyzes peptides between dibasic residues. Trypsin exhibits a high S1 specificity for Arg and Lys residues. However, the S1' specificity of trypsin is very broad, with only a slight preference for hydrophobic residues in P1'. We replaced Lys60 with Glu and Asp to introduce a high specificity for basic residues into the S1' site of trypsin. Both mutations cause a dramatic increase in the S1' specificity for Arg and Lys as measured by acyl transfer reactions. In K60E, the preference for Arg increases 70-fold while the preference for P1'-Lys increases 12-fold. In contrast, the preferences for other P1' residues either decrease slightly or remain the same. Thus, K60E prefers P1'-Arg over most other P1' residues by 2 orders of magnitude. Similar results are obtained when P1' specificity is measured in peptide cleavage assays. K60D exhibits an S1' specificity profile very similar to that of K60E, although the P1'-Arg preference is reduced by a factor of 2.5. Molecular modeling studies suggest that the high S1' specificity for Arg in K60E may be due to the formation of a salt bridge between Glu60 and the P1'-Arg of the substrate.


Subject(s)
Amino Acids, Diamino/metabolism , Protein Engineering , Trypsin/chemical synthesis , Trypsin/metabolism , Animals , Arginine/metabolism , Aspartic Acid/metabolism , Binding Sites/genetics , Crystallography, X-Ray , Glutamic Acid/metabolism , Hydrolysis , Kinetics , Lysine/metabolism , Models, Molecular , Mutagenesis, Site-Directed , Rats , Structure-Activity Relationship , Substrate Specificity/genetics , Trypsin/genetics
13.
J Med Chem ; 40(10): 1530-8, 1997 May 09.
Article in English | MEDLINE | ID: mdl-9154974

ABSTRACT

A series of substituted 4-phenyl-1,4-dihydropyridines 2a-m was tested for their inhibitory effects on L-triiodothyronine (L-T3) uptake by human HepG2 hepatoma cells. The most potent compounds were the nitro-substituted derivatives 2,6-dimethyl-4-(4'-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid 3-ethyl ester 5-methyl ester (2m) and the well-known calcium antagonists nitrendipine (2k) and nifedipine (2j) with an uptake inhibition between 80.5 and 85.8% at an application dose of 10(-5) M. On the basis of a theoretical conformational analysis (ab initio MO theory, molecular mechanics, molecular dynamics) of the dihydropyridine derivatives, a unifying stereochemical concept was derived postulating an angular arrangement of the two rings where the phenyl ring of the calcium antagonists, which corresponds to the outer phenyl ring of the thyroid hormones, is bisecting the dihydropyridine ring as a prerequisite for inhibitory potency. This model includes also inhibitors of the N-phenylanthranilic acid type. The interaction of the calcium antagonists with transthyretin (TTR) is discussed in relation to thyroid hormones. The influence of hydrophobicity was estimated by the experimental determination of the 1-octanol/water partition coefficients.


Subject(s)
Antithyroid Agents/pharmacology , Calcium Channel Blockers/pharmacology , Dihydropyridines/pharmacology , Triiodothyronine/metabolism , Antithyroid Agents/chemistry , Calcium Channel Blockers/chemistry , Dihydropyridines/chemistry , Humans , Structure-Activity Relationship , Triiodothyronine/chemistry , Tumor Cells, Cultured
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