Gelation of xanthan with trivalent metal ions

In-situ gelation of semidilute xanthan solutions with trivalent chromium, aluminum or iron ions was studied by rheology and UV-spectroscopy. Measurements of the elastic modulus of xanthan gel cylinders prepared by dialysis against the complexing ion at pH values from 2 to 6 indicate that monomeric species of the ion are ineffective, whereas dimeric or higher oligomeric species are effective in crosslinking the polysaccharide. When chromium was used as the crosslinking species, the dependence of the gelation rate on the ionic concentration followed a power law with a coefficient of 1·7. The gelation time and the gelation rate were found to extrapolate to zero at 1 m Cr for 2·5 mg/ml xanthan. The limiting concentration of xanthan needed for gelation with 5 m Cr(III) at 20°C was estimated as 0·35 mg/ml. This critical xanthan concentration is close to the overlap concentration c^* estimated from the experimentally determined intrinsic viscosity [η] using c^* = 1·4/[η]. An apparent activation energy for crosslinking of xanthan was calculated as E_a = 42 kJ/mol and E_a = 108 kJ/mol for Cr and Al ions, respectively. The fractal dimensionality of xanthan-Cr at the sol-gel transition was estimated as 1·3 applying the Chambon-Winter criterion for gelation, thus indicating that this gelation criterion is applicable also to stiff-chain polysaccharides such as xanthan.     

Stereochemistry and size of sugar head groups determine structure and phase behavior of glycolipid membranes: densitometric, calorimetric, and X-ray studies

The role carbohydrate moieties play in determining the structure and energetics of glycolipid model membranes has been investigated by small- and wide-angle X-ray scattering, differential scanning densitometry (DSD), and differential scanning microcalorimetry (DSC). The dependence of a variety of thermodynamic and structural parameters on the stereochemistry of the OH groups in the pyranose ring and on the size of the sugar head group has been studied by using an homologous series of synthetic stereochemically uniform glyceroglycolipids having glucose, galactose, mannose, maltose, or trimaltose head groups and saturated ether-linked alkyl chains with 10, 12, 14, 16, or 18 carbon atoms per chain. The combined structural and thermodynamic data indicate that stereochemical changes of a single OH group in the pyranose ring can cause dramatic alterations in the stability and in the nature of the phase transitions of the membranes. The second equally important determinant of lipid interactions in the membrane is the size of the head group. A comparison of lipids with glucose, maltose, or trimaltose head groups and identical hydrophobic moieties has shown that increasing the size of the neutral carbohydrate head group strongly favors the bilayer-forming tendency of the glycolipids. These experimental results provide a verification of the geometric model advanced by Israelachvili et al. (1980) [Israelachvili, J. N., Marcelja, S., & Horn, R. G. (1980) Q. Rev. Biophys. 13, 121-200] to explain the preferences lipids exhibit for certain structures. Generally galactose head groups confer highest stability on the multilamellar model membranes as judged on the basis of the chain-melting transition. This is an interesting aspect in view of the fact that galactose moieties are frequently observed in membranes of thermophilic organisms. Glucose head groups provide lower stability but increase the number of stable intermediate structures that the corresponding lipids can adopt. Galactolipids do not even assume a stable intermediate L alpha phase for lipids with short chain length but perform only Lc----HII transitions in the first heating. The C2 isomer, mannose, modifies the phase preference in such a manner that only L beta----HII changes can occur. Maltose and trimaltose head groups prevent the adoption of the HII phase and permit only L beta----L alpha phase changes. The DSD studies resulted in a quantitative estimate for the volume change associated with the L alpha----HII transition of 14-Glc. The value of delta v = 0.005 mL/g supports the view that the volume difference between L alpha and HII is minute.(ABSTRACT TRUNCATED AT 400 WORDS)     

The clinical significance of HAMA in patients treated with mouse monoclonal antibodies

Twenty-four patients were analyzed for the development of HAMA (human antimouse antibodies) after being treated with repeated doses (200–500 mg) of the mouse monoclonal antibody (MAb) 17-1A. All patients developed anti-17-1A IgG antibodies, and most of them also developed IgM antibodies. In only two patients could immune complexes be demonstrated. Allergic reactions were rare (1.9%). In an extended study, a further 19 patient were analyzed for an idiotypic response. Forty-one out of 43 patients developed antiidiotypic antibodies (ab₂), and 20 of these also antianti-idiotypic antibodies (ab₃). Ab₃ ⁺ patients responded significantly better (p=0.01) and survived longer (p<0.001) compared to ab₃ ⁻ patients. In this study, we showed that MAb 17-1A could be repeatedly given on a safe basis. The development of high titers of HAMA did not cause significant clinical problems when further repeated infusions of MAb 17-1A were given. The development of an idiotypic response also indicate that the induction of HAMA might be beneficial and not harmful to the patient.     

Le Crocodilien Diplocynodon (Eusuchia,Alligatoridae) dans la«série du gypse d'Aix à Venelles (Bouches-du-Rhône,France)

A crocodilian skeleton from the «série du gypse d'Aix (basal Aquitanian) at Venelles (Bouches-du-Rhône) is described and referred to Diplocynodon cf. rateli. The specimen seems to have been mutilated by scavengers before burial. The occurrence of the freshwater crocodilian Diplocynodon in the «série du gypse d'Aix is in agreement with recent reconstructions of the depositional environment, which suggest a basin with a fluctuating, but usually low, salinity.     

Cloning and expression of bacteriophage SP02 DNAZ polymerase gene L in Bacillus subtilis, using the Staphylococcus aureus plasmid pC194

HindIII restriction endonuclease fragments of DNA from temperate Bacillus subtilis bacteriophage SP02 were cloned in B. subtilis by using the plasmid pC194. Three hybrid plasmids which permit growth of the mutant SP02 susL244 in suppressor-negative bacteria were isolated. SP02 gene L is thought to code for a DNA polymerase essential for autonomous replication of SP02 DNA. Extracts of bacteria carrying one of these hybrid plasmids, pC194-96, had 10- to 30-fold increased DNA polymerase activity. The plasmid-induced DNA polymerase activity differed from that of the known B. subtilis DNA polymerases in several respects. The results of the experiments support the idea that phage SP02 codes for a new DNA polymerase.     

Spore ultrastructure in Sporothrix schenckii

Pathogenic strains of Sporothrix schenkii may show triangular spores, whose angular shape is maintained by a tiebeam effect in the inner cell wall structure. This difference in wall structure lies adjacent to a folded and possibly more active part of the spore cytoplasm. The supposed generation of asci in old cultures was simulated by the death of hyphae which are reinvaded by intrahyphal growth with intrahyphal spore production, while true asci were not seen.     

The role of displacement of the mitral annulus in left atrial filling and emptying in the intact dog

The variations in ventricular-atrial mitral annular position during the cardiac cycle and the simultaneous changes in left atrial silhouette area (obtained by angiography after injections of contrast material into the main pulmonary artery) were investigated in six experiments on intact dogs with chronically implanted intracardiac markers. Frame-by-frame measurements of the angiograms (120 frames/s) were used to determine, under various hemodynamic conditions, the duration, magnitude, and average rate of the mitral annular motion and of the simultaneous changes in left atrial area during atrial filling (ventricular systole) and atrial emptying (early in ventricular diastole). The mitral annulus was seen to move towards the ventricular apex during systole and towards the atrium early in diastole with the duration, average rate, and magnitude of displacement (although varying widely) showing good statistical correlations (P less than 0.0005-0.005) with the changes in projected left atrial area. These findings suggest that the duration, rate, and magnitude of atrial filling and emptying may be, in the intact heart, determined by the movements of the atrioventricular junction.     

Ants impact the composition of the aquatic macroinvertebrate communities of a myrmecophytic tank bromeliad

In an inundated Mexican forest, 89 out of 92 myrmecophytic tank bromeliads (Aechmea bracteata) housed an associated ant colony: 13 sheltered Azteca serica, 43 Dolichoderus bispinosus, and 33 Neoponera villosa. Ant presence has a positive impact on the diversity of the aquatic macroinvertebrate communities (n = 30 bromeliads studied). A Principal Component Analysis (PCA) showed that the presence and the species of ant are not correlated to bromeliad size, quantity of water, number of wells, filtered organic matter or incident radiation. The PCA and a generalized linear model showed that the presence of Azteca serica differed from the presence of the other two ant species or no ants in its effects on the aquatic invertebrate community (more predators). Therefore, both ant presence and species of ant affect the composition of the aquatic macroinvertebrate communities in the tanks of A. bracteata, likely due to ant deposition of feces and other waste in these tanks.