R-factor-mediated suppression of the galactose-sensitive phenotype of Escherichia coli K-12 galE mutants

Plasmids S-a and Rts1 suppress the galactose-sensitive phenotype of galE mutants of Escherichia coli K-12, giving rise to both galactose-fermenting and nonfermenting strains. Fermenting strains produce normal inducible UDP-galactose epimerase. Plasmids extracted from either a fermenting or a nonfermenting strain are indistinguishable when examined by either measurements of length of relaxed circular molecules by electron microscopy or electrophoretic pattern of restriction endonuclease digestion products. The phenomenon could be explained by reversible recombination between a plasmid-borne epimerase gene and homologous chromosomal sequences.     

Effect of neurotensin on pancreatic function in man

The effect of neurotensin on submaximally-stimulated hepatobiliary and pancreatic secretion was studied in 6 healthy subjects. An intravenous infusion of neurotensin 1.4 ± 0.3 pmol/kg/min, designed to reproduce plasma neurotensin immunoreactivity levels within the physiological range, produced a significant increase in pancreatic bicarbonate output. Plasma concentrations of pancreatic polypeptide rose by 83 ± 16 pmol/l and were associated with a small reduction in trypsin, but no significant change in bilirubin outputs.     

Mechanism of action of rifamazine, a member of a new class of (dimeric) rifamycins.

1. Rifamazine (AF/RP) a dimeric rifamycin, is active against bacterial DNA-dependent RNA polymerase and against viral RNA-dependent DNA polymerase. 2. Rifamazine is active also against DNA-dependent RNA polymerase extracted from rifampicin-resistant mutants of Escherichia coli. It does not interfere with enzyme-template interaction or with RNA elongation. It blocks initiation. 3. A comparison is made between the mechanism of action of rifamazine and that of rifampicin, and of AF/013 (octyloxime of 3-formylrifamycin SV), a C-class rifamycin. Our results show that the mechanism of action of rifamazine is more similar to that of rifampicin than to that of the octyloxime derivative. 4. Activity of rifamazine against RNA polymerase from rifampicin-resistant mutants is thought to be due to binding of the dimer to both the rifamycin-specific binding site and to a second weak site.     

Effect of Metalaxyl on the incidence and severity of Pearl millet downy mildew disease in Northern Nigeria

Pearl millet downy mildew (DM) incidence, severity and yield losses of two pearl millet varieties (local and improved) due to the disease were determined in the field. Significant differences in the disease incidence and severity were recorded in the plots sown with metalaxyl-treated seeds and those sown with non-treated seeds, indicating the efficacy of the fungicide on the fungus. Yield losses due to non-treatment of seeds with metalaxyl was 40.88 and 45.39% in a local variety and 43.00 and 18.60% in an improved variety in the 2000 and 2001 cropping seasons respectively. Significant differences between plots sown with metalaxyl-treated and those sown with non-treated seeds were obtained for other yield components such as 1000-grains weight, panicle length and weight.     

Effect of temperature on the saccharide composition obtained after alpha-amylolysis of starch

The hydrolysis of starch to low-molecular-weight products (normally characterised by their dextrose equivalent (DE), which is directly related to the number-average molecular mass) was studied at different temperatures. Amylopectin potato starch, lacking amylose, was selected because of its low tendency towards retrogradation at lower temperatures. Bacillus licheniformis alpha-amylase was added to 10% [w/w] gelatinised starch solutions. The hydrolysis experiments were done at 50, 70, and 90 degrees C. Samples were taken at defined DE values and these were analysed with respect to their saccharide composition. At the same DE the oligosaccharide composition depended on the hydrolysis temperature. This implies that at the same net number of bonds hydrolysed by the enzyme, the saccharide composition was different. The hydrolysis temperature also influenced the initial overall molecular-weight distribution. Higher temperatures led to a more homogenous molecular weight distribution. Similar effects were observed for alpha-amylases from other microbial sources such as Bacillus amyloliquefaciens and Bacillus stearothermophilus. Varying the pH (5.1, 6.2, and 7.6) at 70 degrees C did not significantly influence the saccharide composition obtained during B. licheniformis alpha-amylase hydrolysis. The underlying mechanisms for B. licheniformis alpha-amylase were studied using pure linear oligosaccharides, ranging from maltotriose to maltoheptaose as substrates. Activation energies for the hydrolysis of individual oligosaccharides were calculated from Arrhenius plots at 60, 70, 80, and 90 degrees C. Oligosaccharides with a degree of polymerisation exceeding that of the substrate could be detected. The contribution of these oligosaccharides increased as the degree of polymerisation of the substrate decreased and the temperature of hydrolysis increased. The product specificity decreased with increasing temperature of hydrolysis, which led to a more equal distribution between the possible products formed. Calculations with the subsite map as determined for the closely related alpha-amylase from B. amyloliquefaciens reconfirmed this finding of a decreased substrate specificity with increased temperature of hydrolysis. Copyright 1999 John Wiley & Sons, Inc.