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81.
Benedetti Ettore Iacovino Rosa Pedone Carlo Rossi Filomena Saviano Michele Isernia Carla Montesarchio Daniela de Napoli Lorenzo Piccialli Gennaro 《International journal of peptide research and therapeutics》1997,4(3):129-134
Summary An N- and C-protected derivative ofhomo-β-leucine, Fmoc-homo-β-(S)-leucine methyl ester, synthesized from the corresponding proteinogenic parent α-amino acid in enantiopure form has been
fully characterized in the solid state by X-ray diffraction analysis. The crystal conformation of this new residue indicates
and extended conformation for thishomo-β-residue, with the ϕ torsion angle being more constrained than the μ and ψ angles. 相似文献
82.
《Bioorganic & medicinal chemistry》2016,24(21):5340-5352
γ-Glutamyl transpeptidase (GGT, EC 2.3.2.2) that catalyzes the hydrolysis and transpeptidation of glutathione and its S-conjugates is involved in a number of physiological and pathological processes through glutathione metabolism and is an attractive pharmaceutical target. We report here the evaluation of a phosphonate-based irreversible inhibitor, 2-amino-4-{[3-(carboxymethyl)phenoxy](methoyl)phosphoryl}butanoic acid (GGsTop) and its analogues as a mechanism-based inhibitor of human GGT. GGsTop is a stable compound, but inactivated the human enzyme significantly faster than the other phosphonates, and importantly did not inhibit a glutamine amidotransferase. The structure–activity relationships, X-ray crystallography with Escherichia coli GGT, sequence alignment and site-directed mutagenesis of human GGT revealed a critical electrostatic interaction between the terminal carboxylate of GGsTop and the active-site residue Lys562 of human GGT for potent inhibition. GGsTop showed no cytotoxicity toward human fibroblasts and hepatic stellate cells up to 1 mM. GGsTop serves as a non-toxic, selective and highly potent irreversible GGT inhibitor that could be used for various in vivo as well as in vitro biochemical studies. 相似文献
83.
The aim of this study was to investigate organophosphorus pesticides (OPs) concentrations in rice grains and estimate potential health risk to inhabitants. A total of 102 rice samples were collected from the Irrigated Area of Songhua River, located in Jilin province, one of the most important rice production areas and a key agricultural area in China. The twelve OPs were determined by gas chromatography coupled with flame photometric detector. Results showed that OPs concentrations in rice grains did not exceed maximum residue limit. The mean concentrations obtained for the detected twelve OPs in µg kg?1 were as follows: omethoate (0.60), diazinon (0.56), parathion-methyl (0.54), dimethoate (0.38), isocarbophos (0.38), phorate (0.31), fenitrothion (0.24), parathion (0.23), fenthion (0.23), malathion (0.13), dichlorvos (0.13), and methamidophos (0.08). Diazinon (39.2%), omethoate (31.4%), and parathion-methyl (25.5%) had the highest frequency in the detected twelve OPs. 69.6% of samples contained more than one OP, 24.5% of samples detected one OP, and only 5.9% samples did not find any OPs. The average target hazard quotients were all less than one and average hazard index for adults and children were 0.273 and 0.238, respectively. Overall, results indicated that the intake of rice may be safe for consumers. 相似文献
84.
The pesticides carbendazim (CA), imidacloprid (IM), and thiophanate-methyl (TH) are used extensively in apple production. However, the presence of pesticide residues in apples has been associated with a wide range of human health hazards. To assess whether apples are safe to consume, evaluating their potential health risk is of great significance. We tested apples from two dominant apple-producing areas for the presence of pesticide residues and constructed a statistical model to evaluate their health risks. Of the three commonly used pesticides, thirty-two samples (11.3% of all tested samples) were residue-free and 231 (81.9%) contained CA residues, which was the most frequently detectable pesticide, followed by TH (52.1%) and IM (39.0%). All of the samples were below the maximum residue limits. The probabilistic assessment results indicated that the pesticide intake risks for kids (aged 2–6 years) and children (aged 7–13 years) were significantly higher than those of other groups, so that they were the vital monitoring objects. Our findings indicate that consumption of apples with these three pesticides does not pose a health threat for the population. Nevertheless, we recommend an investigation into continuous monitoring and stricter regulations on fruits' quality and safety throughout China. 相似文献
85.
Whitbread Anthony Blair Graeme Naklang Kunnika Lefroy Rod Wonprasaid Sodchol Konboon Yothin Suriya-arunroj Duangjai 《Plant and Soil》1999,207(1):29-36
The maintenance of soil organic matter (SOM) and the balancing of nutrient flows into and out of the rainfed rice cropping
systems in Northeast Thailand is of paramount importance to arresting the decline in soil fertility and crop yields. A system
where small applications of leaf litters from locally grown trees are applied annually to rice paddy soils prior to transplanting
is described. The annual application of 1500 kg/ha of Cajanus cajan, Acacia auriculiformis, Phyllanthus taxodifolius and Samanea
saman for five seasons resulted in increases in rice grain yield of 48, 35, 32 and 23% above the no-leaf litter control, respectively.
Average annual nutrient inputs from the leaf litters, in kg/ha, ranged from 62.7 N, 3.9 P, 17.9 K, and 3.5 S for Cajanus cajan
to 24.5 N, 1.5 P, 8.1 K and 2.0 S for Acacia auriculiformis. Nutrient balances, determined by the difference between the inputs
(fertiliser and added leaf litters) and outputs (grain and straw) indicated net positive N and P balances of up to 457 and
60 kg/ha. respectively, after five seasons of leaf litter applications. Sulfur and potassium balances resulted in net deficits
of up to −3 and −52 kg S and K/ha, respectively, where no leaf litter was applied and rice straw was removed following harvest.
Calculated apparent nutrient recoveries reflected the decomposition rate of the added residues and were highest for P and
K, reflecting their higher soil residual value than mobile nutrients such as N and S. Sustainable farming systems will require
that crop yields are stable through the maintenance of soil fertility and the balance of nutrients in the system.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
86.
Essential arginine residues are suggested to be located at the active sites of maize branching enzymes (BE) based on the evidence that two arginine residues are conserved in all BE from various species and that as little as one arginine residue is located at the active site of maize BE by phenylglyoxal (PGO) modification. To determine the exact location of the active-site arginine residue in BE, we employed peptide mapping and site-directed mutagenesis approaches. A single trypsin-digested, [14C]PGO-labeled peptide was purified from maize BEII by two rounds of HPLC separation, but we failed to obtain amino acid sequencing information. Site-directed mutagenesis was then used to create one mutant (arginine-384 to alanine-384), R384A. Immunoblotting result showed that BEII protein was expressed at a similar level in the wild type and the R384A mutant. However, BE activity in the R384A mutant was only 1.4% of the wild type. These results support the conclusion that the conserved arginine-384 residue is important in BEII catalysis. 相似文献
87.
Search and study of the general principles that govern kinetics and thermodynamics of protein folding generate a new insight into the factors controlling this process. Here, based on the known experimental data and using theoretical modeling of protein folding, we demonstrate that there exists an optimal relationship between the average conformational entropy and the average energy of contacts per residue-that is, an entropy capacity-for fast protein folding. Statistical analysis of conformational entropy and number of contacts per residue for 5829 protein structures from four general structural classes (all-alpha, all-beta, alpha/beta, alpha+beta) demonstrates that each class of proteins has its own class-specific average number of contacts (class alpha/beta has the largest number of contacts) and average conformational entropy per residue (class all-alpha has the largest number of rotatable angles phi, psi, and chi per residue). These class-specific features determine the folding rates: alpha proteins are the fastest folding proteins, then follow beta and alpha+beta proteins, and finally alpha/beta proteins are the slowest ones. Our result is in agreement with the experimental folding rates for 60 proteins. This suggests that structural and sequence properties are important determinants of protein folding rates. 相似文献
88.
89.
Nicholas Cox Naray Pewnim Paul J. Smith Joseph L. Hughes Stenbjörn Styring Ron J. Pace 《BBA》2009,1787(7):882-889
Detailed optical and EPR analyses of states induced in dark-adapted PS II membranes by cryogenic illumination permit characterization and quantification of all pigment derived donors and acceptors, as well as optically silent (in the visible, near infrared) species which are EPR active. Near complete turnover formation of QA− is seen in all centers, but with variable efficiency, depending on the donor species. In minimally detergent-exposed PS II membranes, negligible (< 5%) oxidation of chlorophyll or carotenoid centers occurs for illumination temperatures 5-20 K. An optically silent electron donor to P680+ is observed with the same decay kinetics as the S1 split signal. Cryogenic donors to P680+ seen are: (i) transient (t1/2 ∼ 150 s) tyrosine related species, including ‘split signals’ (∼ 15% total centers), (ii) reduced cytochrome b559 (∼ 30-50% centers), and (iii) an organic donor, possibly an amino acid side chain, (∼ 30% centers). 相似文献
90.