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D J Nicholas

Publications and source records attributed to D J Nicholas.

At least 37 records · Page 2Linked to original sources
PubMed1978

Effects of amino acids, adenine nucleotides and inorganic pyrophosphate on glutamine synthetase from Anabaena cylindrica.

Glutamine synthetase (L-glutamate:ammonia ligase (ADP-forming), EC 6.3.1.2) from Anabaena cylindrica was inhibited by alanine, glycine, serine and aspartate. The effects of alanine and serine were uncompetitive with respect to glutamate, while those of glycine and asparatate were uncompetitive with respect to glutamate, while those of glycine and aspartate were non-competitive and mixed type respectively. Different pairs of amino acids and their various combinations caused a cumulative inhibition of the enzyme activity. Glutamine synthetase was also inhibited by ADP and AMP and both nucleotides affected the enzyme competitively with respect to ATP and non-competitively for glutamate. Inorganic pyrophosphate, between 2 and 3 mM, produced a very pronounced inhibiton of enzyme activity. The inhibition by PPi was uncompetitive for ATP. Various combinations of the adenine nucleotides, PPi and Pi exerted a cumulative inhibitory effect on the enzyme activity, as did the amino acids, in different combinations with either adenine nucleotides, PPi or Pi. The effects of the adenine nucleotides and the amino acids were more pronounced at higher concentrations of ammonia. Except for serine similar responses of these effectors were obtained with increasing concentrations of Mg2+. It is proposed that changes in the free concentrations of Mg2+ are important in energy-dependent regulation of the enzyme activity in this alga.

Adenine Nucleotides↗
PubMed1977

Proton translocation in intack cells of Thiobacillus denitrificans.

Proton translocation assessed by the quinacrine fluorescence technique was compared with oxygen uptake during thiosulphate oxidation by cells of Thiobacillus denitrificans. The addition of thiosulphate to cell suspensions resulted in an outwardly directed proton translocation as reflected by an increased quinacrine fluorescence. Compared to the O2 uptake activity, the proton translocating system was much more sensitive to proton conductors, other ionophores and inhibitors of electron transport. The results indicate that (a) the proton-translocation activity (membrane energization) is enhanced in aged cell suspensions, (b) intactness of the cytoplasmic membrane is essential for establishing a protonmotive force in cells, (c) the fluorescence increase and proton translocation are reversible processes, (d) inhibitors of electron transport may also act as proton conductors by altering the integrity of the cytoplasmic membrane.

Cell Membrane↗
PubMed1977

Effects of adenine nucleotides and phosphate on adenosine triphosphate sulphurylase from Anabaena cylindrica.

Production of adenosine 5'-[35S]sulphatophosphate by a partially purified ATP sulphurylase from Anabaena cylindrica was inhibited by AMP, ADP and P1. Decreases in enzyme activity in the presence of these inhibitors were reversed by increasing the concentrations of ATP. The adenine nucleotides inhibited the enzyme competitively with respect to ATP. In the presence of P1, ATP showed a positive co-operative effect on enzyme activity. The inhibition by P1 was enhanced by increasing concentrations of MG2+. The effects of the adenine nucleotides and the interaction of P1 and Mg2+ on ATP sulphurylase activity are discussed in relation to the regulation of sulphate assimilation via the energy metabolism of the alga.

Adenine Nucleotides↗
PubMed1976

Utilization of 35S-thiosulphate and an appraisal of the role of ATP-sulphurylase in chemolithotrophic Thiobacillus ferrooxidans.

Differentially labelled 35S-thiosulphate was taken up by washed cells of Thiobacillus ferrooxidans which were previously grown on thiosulphate. The uptake was proportional to the biomass over the range 0.5-4.0 mg dry wt. of bacteria and showed typical saturation kinetics with an estimated Km value of 0.5 mM for 35S-thiosulphate. Dithionate and Group VI anions inhibited the uptake, which was under pH control and had a temperature optimum of 50 degrees C. In the absence of thiosulphate, the cells bound 35S-sulphate but the binding did not increase on prolonged incubation and the label could be removed completely by washing with dilute sulphuric acid. Increasing amounts of the label were incorporated from [outer-35S]thiosulphate into cellular materials over a 60-min period, whereas little or no assimilation was observed from either the [inner-35S]thiosulphate or 35S-sulphate. The kinetic properties of the sulphate-activating enzyme ATP-sulphurylase enriched from bacteria grown with either thiosulphate or ferrous-iron were similar although this enzyme has an assimilatory function only when the bacterium is grown with ferrous-iron.

Ferrous Compounds↗
PubMed1976

Degradation of sulphur nucleotides in cell-free extracts of Thiobacillus ferrooxidans.

The cell-free extracts of Thiobacillus ferrooxidans contain hydrolytic enzymes which cleave sulphate from either adenosine 5'-sulphatophosphate or adenosine 3'-phosphate 5'-sulphatophosphate. These sulphatase activities may be retarded by including either phosphates or adenine nucleotides in the incubation mixtures. Adenosine 3'-phosphate 5'-sulphatophosphate and its immediate breakdown product adenosine 3'-phosphate 5'-phosphate were degraded at slower rates than adenosine 5'-sulphatophosphate.

Adenine Nucleotides↗
PubMed1976

Enzymic comparisons of the inorganic sulfur metabolism in autotrophic and heterotrophic Thiobacillus ferrooxidans.

Activities of enzymes which mediate the oxidation of thiosulfate to sulfate and the assimilation of sulfate to sulfide were assayed in various cell-free fractions of Thiobacillus ferrooxidans grown autotrophically on either ferrous iron or thiosulfate or heterotrophically on glucose. There was no activity of the thiosulfate-oxidizing enzyme in extracts of bacteria grown with ferrous iron. Comparable activities for ATP-sulfurylase (EC 2.7.7.4), ADP-sulfurylase (EC 2.7.7.5), and adenylate kinase (EC 2.7.4.3) were found in the bacteria grown autotrophically with either Fe2+ or S2O32- or heterotrophically with glucose.

Adenosine Triphosphate↗
PubMed1976

Repression, derepression and activation of nitrogenase in Azotobacter vinelandii.

Ammonium ion repressed nitrogenase in cells fixing N2 gas. Immunological tests and electrophoresis in various gels show that components I (Fe-Mo-S protein) was completely repressed by ammonium, whereas component II (Fe-S protein) apoprotein was not markedly affected. Component II from ammonium-grown cells, however, was inactive since it did not cross react with component I to reduce C2H2 to C2H4. The inactive component II apoprotein is immunologically identical to its active counterpart from cells fixing N2. Identical protein patterns were also observed in various gel-electrophoresis systems. Oxygen-inactivated component II may be reactivated with FeSo4. This salt is preferable to ferrous ammonium sulphate which inactivated component I. Immunodiffusion under aerobic conditions shows that purified component I is composed of aggregated and non-aggregated forms which are antigenically distinct. The aggregate was dissociated by treatment with sodium dodecyl sulphate (SDS) into a single antigenic species which was further resolved into two subunits on SDS disc polyacrylamide gel electrophoresis.

Ammonium Chloride↗
PubMed1975

The uptake and assimilation of sulphate by Thiobacillus ferrooxidans.

Sulphate was rapidly bound by cell suspensions of Thiobacillus ferrooxidans. The binding was depressed by tetrathionate but was unaffected by Group VI anions, cysteine or methionine. Increasing uptake of sulphate was observed in cell suspensions incubated in the presence of ferrous iron. The bulk of 35S-sulphate was removed from the organisms by washing with dilute sulphuric acid and the remaining label was incorporated into cold trichloroacetic acid-soluble compounds. 35S-labelled adenosine 5'-sulphatophosphate was produced from ATP and 35S-sulphate by cell suspensions and in cell-free extracts. There was no evidence for the production of adenosine 3'-phosphate 5'-sulphatophosphate assayed by a very sensitive bioluminescence method.

Adenine Nucleotides↗
PubMed1974

The partial characterization of purified nitrite reductase and hydroxylamine oxidase from Nitrosomonas europaea.

Nitrite reductase has been separated from cell-free extracts of Nitrosomonas and partially purified from hydroxylamine oxidase by polyacrylamide-gel electrophoresis. In its oxidized state the enzyme, which did not contain haem, had an extinction maximum at 590nm, which was abolished on reduction. Sodium diethyldithiocarbamate was a potent inhibitor of nitrite reductase. Enzyme activity was stimulated 2.5-fold when remixed with hydroxylamine oxidase, but was unaffected by mammalian cytochrome c. The enzyme also exhibited a low hydroxylamine-dependent nitrite reductase activity. The results suggest that this enzyme is similar to the copper-containing ;denitrifying enzyme' of Pseudomonas denitrificans. A dithionite-reduced, 465nm-absorbing haemoprotein was associated with homogeneous preparations of hydroxylamine oxidase. The band at 465nm maximum was not reduced during the oxidation of hydroxylamine although the extinction was abolished on addition of hydroxylamine, NO(2) (-) or CO. These last-named compounds when added to the oxidized enzyme precluded the appearance of the 465nm-absorption band on addition of dithionite. Several properties of 465nm-absorbing haemoprotein are described.

Ammonium Sulfate↗