Involvement of deacylation in activation of substrate hydrolysis by Drosophila acetylcholinesterase

Insect acetylcholinesterase (AChE), an enzyme whose catalytic site is located at the bottom of a gorge-like structure, hydrolyzes its substrate over a wide range of concentrations (from 2 microm to 300 mm). AChE is activated at low substrate concentrations and inhibited at high substrate concentrations. Several rival kinetic models have been developed to try to describe and explain this behavior. One of these models assumes that activation at low substrate concentrations partly results from an acceleration of deacetylation of the acetylated enzyme. To test this hypothesis, we used a monomethylcarbamoylated enzyme, which is considered equivalent to the acylated form of the enzyme and a non-hydrolyzable substrate analog, 4-oxo-N,N,N-trimethylpentanaminium iodide. It appears that this substrate analog increases the decarbamoylation rate by a factor of 2.2, suggesting that the substrate molecule bound at the activation site (K(d) = 130 +/- 47 microm) accelerates deacetylation. These two kinetic parameters are consistent with our analysis of the hydrolysis of the substrate. The location of the active site was investigated by in vitro mutagenesis. We found that this site is located at the rim of the active site gorge. Thus, substrate positioning at the rim of the gorge slows down the entrance of another substrate molecule into the active site gorge (Marcel, V., Estrada-Mondaca, S., Magné, F., Stojan, J., Klaébé, A., and Fournier, D. (2000) J. Biol. Chem. 275, 11603-11609) and also increases the deacylation step. This results in an acceleration of enzyme turnover.     

Single Nucleotide Polymorphism Genotyping and Distribution of Coxiella burnetii Strains from Field Samples in Belgium

The genotypic characterization of Coxiella burnetii provides useful information about the strains circulating at the farm, region, or country level and may be used to identify the source of infection for animals and humans. The aim of the present study was to investigate the strains of C. burnetii circulating in caprine and bovine Belgian farms using a single nucleotide polymorphism (SNP) technique. Direct genotyping was applied to different samples (bulk tank milk, individual milk, vaginal swab, fetal product, and air sample). Besides the well-known SNP genotypes, unreported ones were found in bovine and caprine samples, increasing the variability of the strains found in the two species in Belgium. Moreover, multiple genotypes were detected contemporarily in caprine farms at different years of sampling and by using different samples. Interestingly, certain SNP genotypes were detected in both bovine and caprine samples, raising the question of interspecies transmission of the pathogen.     

Study of the N-terminal part of peptidic selective NPFF(2) agonists

Neuropeptide FF (NPFF) has been shown to act as an endogenous anti-analgesic peptide. In this paper, several peptide analogs of the selective ligand dNP(NMe)AFLFQPQRF-NH(2) modified in the putative address segment, were designed to be selective NPFF(2) receptor probes, synthesized and assayed. One peptide dA(NMe)AAFLFQPQRF-NH(2) displays a very high affinity for NPFF(2) receptors transfected in CHO cells, and a high selectivity versus NPFF(1) receptors. The exact residues carried in the N-terminal part of the ligands are not decisive to obtain a high affinity only the length of the peptide in itself seems important to create selectivity.     

QTL mapping of partial resistance in winter wheat to Stagonospora nodorum blotch.

Stagonospora nodorum blotch is an important foliar and glume disease in cereals. Inheritance of resistance in wheat appears to be quantitative. To date, breeding of partially resistant cultivars has been the only effective way to combat this pathogen. The partial resistance components, namely length of incubation period, disease severity, and length of latent period, were evaluated on a population of doubled haploids derived from a cross between the partially resistant Triticum aestivum 'Liwilla' and susceptible Triticum aestivum 'Begra'. Experiments were conducted in a controlled environment and the fifth leaf was examined. Molecular analyses were based on bulked segregant analyses using 240 microsatellite markers. Four QTLs were significantly associated with partial resistance components and were located on chromosomes 2B, 3B, 5B, and 5D. The percentage of phenotypic variance explained by a single QTL ranged from 14 to 21% for incubation period, from 16 to 37% for disease severity, and from 13 to 28% for latent period,     

Are natural coordinates a useful tool in modeling planar biomechanical linkages?

The paper analyzes the use of natural coordinates in modeling and simulation of musculoskeletal models of the human body. A biomechanical model of the lower extremity of the human body was constructed for the analysis. It consists of three anatomical segments described by eight natural coordinates located at the joints. The developed model was applied to solve three classic dynamics problems of human motion: inverse dynamics, direct dynamics, and static optimization. The analysis covers the raising of a leg together with; the time characteristics of the resultant net torques at the basic joints of the leg (inverse dynamics), the time histories of natural coordinates and their velocities (direct dynamics) as well as the time-varying muscle force patterns (static optimization). In order to check the numerical efficiency of modeling in the natural coordinates' environment the results were compared with the ones received through generalized coordinates. Some conclusions drawn from this comparison and final remarks referring to the biomechanical identification of the analyzed motor task were included in the paper.