State of polarization changes: Classification and measurement

We propose a standardization procedure that provides a convenient, quantitative and reproducible laboratory-based method for measuring the state of polarization (SOP) fluctuations produced by polarization varying devices. This method is based on the SOP distributions generated by commercial polarization scramblers. We show that these devices generate distributions of the maximum change of the SOP (in a given sample time) that follow Rayleigh statistics, which scale linearly with scrambling frequency and the sample time. We use this procedure to measure the SOP fluctuations in a short length of coiled fiber subject to mechanical perturbations.     

Model for injury to the foreleg of the Thoroughbred racehorse

A discussion is presented of contributing factors to the injury to the foreleg of the Thoroughbred racehorse. The critical part of the step is taken to be the first 10-20 ms after ground contact as the hoof slides forward and stops. Large nonaxial loads associated with the deceleration of the hoof are shown to arise. Results of accelerometer measurements on the hoof of a horse running at racing speed are presented as well as mechanical properties of the racing surface. The mechanical properties of the track surface, the type of shoe, and the degree of fatigue of the horse all work together to determine the level of risk.     

A noncompetitive peptide inhibitor of the nicotinic acetylcholine receptor from Conus purpurascens venom

A paralytic peptide, psi-conotoxin Piiie has been purified and characterized from Conus purpurascens venom. Electrophysiological studies indicate that the peptide inhibits the nicotinic acetylcholine receptor (nAChR). However, the peptide does not block the binding of alpha-bungarotoxin, a competitive nAChR antagonist. Thus, psi-conotoxin Piiie appears to inhibit the receptor at a site other than the acetylcholine-binding site. As ascertained by sequence analysis, mass spectrometry, and chemical synthesis, the peptide has the following covalent structure: HOOCCLYGKCRRYOGCSSASCCQR* (O = 4-trans hydroxyproline; * indicates an amidated C-terminus). The disulfide connectivity of the toxin is unrelated to the alpha- or the alphaA-conotoxins, the Conus peptide families that are competitive inhibitors of the nAChR, but shows homology to the mu-conotoxins (which are Na+ channel blockers).     

Resonance assignment of methionine methyl groups and chi 3 angular information from long-range proton-carbon and carbon-carbon J correlation in a calmodulin-peptide complex

Several simple 3D experiments are used to provide J correlations between methionine C epsilon methyl carbons and either the C gamma H2 protons or C beta and C gamma. The intensity of the J correlations provides information on the size of the three-bond J couplings and thereby on the chi 3 torsion angle. In addition, a simple 3D version of the HMBC experiment provides a sensitive link between the C epsilon H3 methyl protons and C gamma. The methods are demonstrated for a 20 kDa complex between calmodulin and a 26-residue peptide fragment of skeletal muscle myosin light chain kinase.     

Influence of mass transfer and surface ligand heterogeneity on quantitative BIAcore binding data. Analysis of the interaction of NC10 Fab with an anti-idiotype Fab'

The interaction of monovalent Fab fragments of NC10, an antiviral neuraminidase antibody, and the anti-idiotype antibody 3-2G12 has been used as a model system to demonstrate experimentally the influence of non-ideal binding effects on BIAcore binding data. Because the association rate constant for these two molecules was found to be relatively high (about 5 x 10(5) M-1 S-1), mass transfer was recognised as a potential source of error in the analysis of the interaction kinetics. By manipulation of the flow rate and the surface density of the immobilised ligand, however, the magnitude to this error was minimised. In addition, the application of site-specific immobilisation procedures was found to improve considerably the correlation of experimental binding data to the ideal 1:1 kinetic model such that the discrepancy between experimental and fitted curves was within the noise range of the instrument. Experiments performed to measure the equilibrium constant (KD) in solution resulted in a value of similar magnitude to those obtained from the ratio of the kinetic rate constants, even those measured with a heterogeneous ligand or with a significant mass transfer component. For this system, the experimental complexities introduced by covalent immobilisation did not lead to large errors in the KD values obtained using the BIAcore.     

Cloning and expression of an endo-1,3-1,4-beta-glucanase gene from Bacillus macerans in Lactobacillus reuteri

Strains of the gastrointestinal species Lactobacillus reuteri were electrotransformed with plasmid constructs containing the endo-1,3-1,4-beta-glucanase gene (bglM) of Bacillus macerans. The enzyme was expressed and secreted by the lactobacilli. A plasmid construct containing the bglM gene lacking its promoter was derived and was demonstrated to be useful as a promoter probe vector.