Showing papers by "Michael J. Hynes published in 1994"

Reactions of β-ketoamides. Part 1. Kinetics of enolisation of acetoacetamide in water and of acetoacetamide and acetoacetanilide in ethanol–water

Abstract: Kinetic results are reported for the rates of enolisation (ke) of acetoacetamide in water and for acetoacetamide and acetoacetanilide in ethanol–water (70 : 30 v/v) as measured by their rates of halogenation The effects of nickel (II), zinc(II) and acetate on the rates of enolisation are also described Unlike β-diketones, the enolisation of β-ketoamides is acid catalysedThe rates of ketonisation (kf) of the two β-ketoamides have also been investigated using stopped-flow spectrophotometry The keto : enol ratios have been derived using the experimentally measured ke and kf values

Regulatory circuits of the amdS gene of Aspergillus nidulans.

Abstract: TheamdS gene codes for an acetamidase enzyme that hydrolyses acetamide to acetate and ammonium thus providingA. nidulans with a source of carbon and nitrogen. The exceptionally favourable genetics of this system combined with molecular analysis have enabled many regulatory circuits affectingamdS to be identified genetically. Characterization of the regulatory genes and the definition of the cis-acting sites involved have been done using bothin vivo andin vitro mutagenesis. Recent results on the analysis of the system are presented.

Influence of Yucca schidigera preparations on the activity of urease from Bacillus pasteurii

Abstract: Extracts and preparations of the desert plant Yucca schidigera Roezl ex Ortgies (Mohave yucca), family Lillaceae, have a variety of beneficial effects when included in the diet of humans and domestic animals. Such effects include reduced gastrointestinal and faecal ammonia levels. A proposed mode of action is inhibition of microfloral urease (urea amidohydrolase; EC 3.5.1.5). We describe a rigorous method of in vitro urcase assay, in the presence of potential effectors such as Y schidigera preparations, using the phenolindophenol reaction to measure the ammonia product. The urease of Bacillus pasteurii was characterised in order to determine its suitability as a model bacterial urease. K-phosphate, but not K-HEPES or K-citrate, was found to inhibit this bacterial urease, particularly at low pH, as previously reported for other plant and bacterial ureases. B pasteurii urease was found to have a Michaelis-Menten constant, Km, of 10.5 ± 3.2 mM in 150 mM K-HEPES, pH 65 and 0.89 M KCl, total ionic strength = 0.90 M at 30°C. It was therefore concluded that B pasteuriiurease is indeed a typical bacterial urease, suitable for studying the influence of Y schidigera preparations. For comparison, the effects of Y schidigera preparations on the activity of β-galactosidase (β-D-galactoside galactohydrolase; EC 3.2.1.23) from Aspergillus or yzae, an unrelated hydrolase, were also determined. Urease and β-galactosidase were both weakly and non-specifically inhibited, in a fashion linearly related to the concentration of γ schidigera preparation. Linear regression of the relationship between γ schidigera preparation and enzyme activity yielded inhibition ratios of 3.2 ± 0.4 and 5.4 ± 1.6 nkat ml−1 preparation for urease and β-galactosidase respectively. By comparing with reported in vivo rates of urea degradation in mammals it was concluded that the observed inhibitory properties of Y schidigera preparations are much too low to account for their in vivo effects at feed inclusion levels of as little as 100 g tonne−1.