scholarly journals Anthranilate synthase/anthranilate 5-phosphoribosyl 1-pyrophosphate phosphoribosyltransferase from Aerobacter aerogenes

1972 ◽  
Vol 130 (3) ◽  
pp. 847-859 ◽  
Author(s):  
A. F. Egan ◽  
F. Gibson
Keyword(s):  
Escherichia Coli ◽  
Kinetic Studies ◽  
Competitive Inhibitor ◽  
Active Enzyme ◽  
The Other ◽  
Anthranilate Synthase ◽  
Aerobacter Aerogenes ◽  
Auxotrophic Mutants ◽  
Mutant Strains ◽  
Sequential Mechanism

1. Anthranilate synthase and phosphoribosyltransferase from Aerobacter aerogenes purify simultaneously and sediment together on sucrose gradients, showing that they occur as an enzyme aggregate. Both activities of the intact aggregate are subject to inhibition by tryptophan. 2. By using appropriate auxotrophic mutants it was shown that an intact active enzyme aggregate is formed when the components come from separate mutant strains. An intact active aggregate can also be formed when one component is from Escherichia coli and the other from A. aerogenes. 3. Phosphoribosyltransferase of A. aerogenes is active when not in an aggregate with anthranilate synthase, but is not subject to tryptophan inhibition, indicating that the inhibitor site is on the anthranilate synthase component. 4. Anthranilate synthase can be active and sensitive to tryptophan inhibition when complexed with an inactive phosphoribosyltransferase. 5. Kinetic studies on the anthranilate synthase activity show that tryptophan is a competitive inhibitor with respect to chorismate and a non-competitive inhibitor with respect to either glutamine or NH4+ ions. This is consistent with a sequential mechanism of the ordered type in which chorismate is the first reactant.

scholarly journals Hypoxanthine Incorporation Is Nonmutagenic in Escherichia coli

2006 ◽  
Vol 188 (18) ◽  
pp. 6553-6560 ◽  
Author(s):  
Brian Budke ◽  
Andrei Kuzminov
Keyword(s):  
Escherichia Coli ◽  
Nitrous Acid ◽  
Double Mutant ◽  
The Other ◽  
Wild Type ◽  
Purine Base ◽  
Spontaneous Mutagenesis ◽  
Endonuclease V ◽  
Mutant Strains ◽  
Induced Mutagenesis

ABSTRACT Endonuclease V, encoded by the nfi gene, initiates removal of the base analogs hypoxanthine and xanthine from DNA, acting to prevent mutagenesis from purine base deamination within the DNA. On the other hand, the RdgB nucleotide hydrolase in Escherichia coli is proposed to prevent hypoxanthine and xanthine incorporation into DNA by intercepting the noncanonical DNA precursors dITP and dXTP. Because many base analogs are mutagenic when incorporated into DNA, it is intuitive to think of RdgB as acting to prevent similar mutagenesis from deaminated purines in the DNA precursor pools. To test this idea, we used a set of Claire Cupples' strains to detect changes in spontaneous mutagenesis spectra, as well as in nitrous acid-induced mutagenesis spectra, in wild-type cells and in rdgB single, nfi single, and rdgB nfi double mutants. We found neither a significant increase in spontaneous mutagenesis in rdgB and nfi single mutants or the double mutant nor any changes in nitrous acid-induced mutagenesis for rdgB mutant strains. We conclude that incorporation of deaminated purines into DNA is nonmutagenic.

DRIED WHOLE EGG POWDER: XV THE GROWTH OF SALMONELLA AND OTHER ORGANISMS IN LIQUID AND RECONSTITUTED EGG

1944 ◽  
Vol 22f (6) ◽  
pp. 169-173 ◽  
Author(s):  
N. E. Gibbons ◽  
C. O. Fulton ◽  
R. L. Moore
Keyword(s):  
Escherichia Coli ◽  
Staphylococcus Aureus ◽  
Streptococcus Pyogenes ◽  
The Other ◽  
Aerobacter Aerogenes ◽  
Egg Powder ◽  
Whole Egg

Curves are presented showing the growth in liquid egg of Salmonella bareilly, S. manhattan, S. typhi-murium, S. oranienburg, S. typhi, Escherichia coli, Aerobacter aerogenes, Staphylococcus aureus, Streptococcus fecalis and S. pyogenes, and of Salmonella bareilly in reconstituted egg. Streptococcus pyogenes does not grow in egg and dies off rapidly at temperatures above 60° F. (15.6 °C.). The other organisms generally grow well in liquid egg at temperatures above 60° F. (15.6 °C.). Liquid and reconstituted egg should therefore be maintained well below this temperature to prevent the multiplication of Salmonella and other possible pathogens.

MUTATION SPECTRUM IN THE FUNGUS CONIOCHAETA VELUTINA

1969 ◽  
Vol 11 (4) ◽  
pp. 870-879 ◽  
Author(s):  
M. C. Paterson ◽  
H. Tan ◽  
F. Cooke
Keyword(s):  
The Other ◽  
Mutation Spectrum ◽  
Complete Medium ◽  
Auxotrophic Mutants ◽  
Suppressor Mutations ◽  
Mutant Strains

Auxotrophic, morphological, sensitive and suppressor mutant strains of Coniochaeta velutina are described. Of 1334 auxotrophic mutants isolated, all but 58 have been characterized as to their specific requirements. The mutation spectrum obtained on malt medium differs in several respects from that on complete medium. Arginine, adenine, cysteine, methionine, histidine and pyrimidine requiring mutants were most frequently isolated. Of 12 diauxotrophs tested genetically, 7 proved to be double mutants, but the remaining 5 behaved genetically as single mutants with a double requirement. Four of these required both adenine and histidine for growth and the other both phenylalanine and tyrosine. Cysteine-sensitive mutants and histidine-sensitive strains are described. Other mutants isolated included a variety of morphological, conidial and colour variants, UV-sensitive strains, canavanine-sensitive strains and arginine-suppressor mutations.

scholarly journals Kinetic studies with skeletal-muscle hexokinase

1966 ◽  
Vol 100 (3) ◽  
pp. 739-744 ◽  
Author(s):  
CJ Toews
Keyword(s):  
Skeletal Muscle ◽  
Initial Velocity ◽  
Gel Filtration ◽  
Kinetic Studies ◽  
Competitive Inhibitor ◽  
Product Inhibition ◽  
Velocity Analysis ◽  
Sequential Mechanism ◽  
Ammonium Sulphate Fractionation ◽  
Ordered Sequential Mechanism

Rat skeletal-muscle hexokinase was partially purified by ammonium sulphate fractionation and gel filtration. The mechanism of the skeletal-muscle hexokinase was studied kinetically by initial-velocity analysis and product inhibition. Glucose 6-phosphate was a non-competitive inhibitor of glucose and ATP. ADP was a non-competitive inhibitor of glucose and a competitive inhibitor of ATP. The data on product inhibition and initial-velocity analysis of skeletal-muscle hexokinase support an ordered sequential mechanism (ordered Bi Bi) where the addition of substrates and release of products is in the order: ATP, glucose, glucose 6-phosphate and ADP.

Mechanism of competition between chloride and stilbenedisulfonates for binding to human erythrocyte band 3 (AE1)

1998 ◽  
Vol 76 (5) ◽  
pp. 715-722 ◽  
Author(s):  
James M Salhany
Keyword(s):  
Human Erythrocyte ◽  
Plasma Membranes ◽  
Kinetic Studies ◽  
Cell Types ◽  
Competitive Inhibitor ◽  
Band 3 ◽  
Red Cell Membrane ◽  
Competitive Inhibitors ◽  
Sequential Mechanism ◽  
Resealed Ghosts

Stilbenedisulfonates (S) constitute an important class of competitive inhibitors of the anion exchange (AE) function found in plasma membranes of various cell types. I present a brief summary of recent kinetic studies that provide insight into the mechanism of stilbenedisulfonate-chloride competition in binding to human erythrocyte band 3 (AE1) (B), the chloride-bicarbonate exchanger. Reversible stilbenedisulfonate binding follows a two-step mechanism (S + B <–> SB <–> SB*). Several lines of evidence are summarized that show that chloride, stilbenedisulfonates, and band 3 form a ternary complex, with chloride lowering stilbenedisulfonate affinity allosterically, by accelerating the rate of stilbenedisulfonate release. Of particular significance was our evidence demonstrating that extracellular chloride could accelerate stilbenedisulfonate release from its binding site on the outer surface of band 3 in resealed ghosts (i.e., acceleration in the release of a bound competitive inhibitor by a cis substrate). I suggest that the latter result may be consistent with our earlier proposal that band 3 follows a two-site ordered sequential mechanism, where two allosterically linked chloride binding transport sites move back and forth across the membrane together.Key words: band 3, anion transport, red cell membrane, membrane proteins.

Infection of Escherichia coli with bacteriophages

1969 ◽  
Vol 27 ◽  
pp. 370-371
Author(s):  
Manfred E. Bayer
Keyword(s):  
Escherichia Coli ◽  
Nucleic Acid ◽  
Cell Surface ◽  
Virus Type ◽  
Infection Process ◽  
Adsorption Site ◽  
The Other ◽  
Specific Receptors ◽  
Bacterial Receptors

The first step in the infection of a bacterium by a virus consists of a collision between cell and bacteriophage. The presence of virus-specific receptors on the cell surface will trigger a number of events leading eventually to release of the phage nucleic acid. The execution of the various "steps" in the infection process varies from one virus-type to the other, depending on the anatomy of the virus. Small viruses like ØX 174 and MS2 adsorb directly with their capsid to the bacterial receptors, while other phages possess attachment organelles of varying complexity. In bacteriophages T3 (Fig. 1) and T7 the small conical processes of their heads point toward the adsorption site; a welldefined baseplate is attached to the head of P22; heads without baseplates are not infective.

The Nature of the Intramembrane Particle

1980 ◽  
Vol 38 ◽  
pp. 688-691
Author(s):  
A.J. Verkleij
Keyword(s):  
Escherichia Coli ◽  
Tight Junction ◽  
Gap Junction ◽  
The Other ◽  
Fracture Face ◽  
Band 3 Protein ◽  
Satisfactory Explanation ◽  
Freeze Fracturing ◽  
Intramembrane Particle ◽  
Luminal Membrane

Freeze-fracturing splits membranes into two helves, thus allowing an examination of the membrane interior. The 5-10 rm particles visible on both monolayers are widely assumed to be proteinaceous in nature. Most membranes do not reveal impressions complementary to particles on the opposite fracture face, if the membranes are fractured under conditions without etching. Even if it is considered that shadowing, contamination or fracturing itself might obscure complementary pits', there is no satisfactory explanation why under similar physical circimstances matching halves of other membranes can be visualized. A prominent example of uncomplementarity is found in the erythrocyte manbrane. It is wall established that band 3 protein and possibly glycophorin represents these nonccmplanentary particles. On the other hand a number of membrane types show pits opposite the particles. Scme well known examples are the ";gap junction',"; tight junction, the luminal membrane of the bladder epithelial cells and the outer membrane of Escherichia coli.

Peroxidases from Tulip Bulbs (Tulipa fosteriana, L.) Oxidize Xenobiotics NNitrosodimethylamine and N-Nitroso-N-methylaniline in vitro

1997 ◽  
Vol 62 (11) ◽  
pp. 1804-1814 ◽  
Author(s):  
Marie Stiborová ◽  
Hana Hansíková
Keyword(s):  
Cytochromes P450 ◽  
Kinetic Studies ◽  
The Other ◽  
Maximal Velocity ◽  
Michaelis Constant ◽  
Other Hand ◽  
Plant Peroxidases ◽  
Tulip Bulbs

Tulip bulbs (Tulipa fosteriana, L.) contain peroxidases catalyzing the oxidation of the xenobiotics N-nitrosodimethylamine (NDMA) and N-nitroso-N-methylaniline (NMA). Three anionic (A1, A2, A3) and four cationic (B, C, D, E) peroxidases were purified from this tissue, partially characterized and used for kinetic studies. Demethylation of NDMA and NMA producing formaldehyde is catalyzed by one anionic (A1) and three cationic (C, D, E) peroxidases. The oxidation of NDMA by tulip peroxidases exhibits the Michaelis-Menten kinetics. The apparent Michaelis constant and the maximal velocity values for this substrate were determined. On the other hand, non-Michaelian kinetics for the NMA oxidation were observed with tulip peroxidases. The most abundant cationic peroxidase (peroxidase C) was used for detailed enzymatic studies. In addition to formation of formaldehyde, methylaniline, aniline, 4-aminophenol and phenol were found to be metabolites formed from NMA. Phenol was formed presumably by N-demethylation via a benzenediazonium ion, while methylaniline, aniline and 4-aminophenol were products of denitrosation of the substrate. The efficiencies of plant peroxidases to oxidize NDMA and NMA in vitro are compared with those of cytochromes P450 and discussed.

scholarly journals Lac Operon Boolean Models: Dynamical Robustness and Alternative Improvements

Mathematics ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 600 ◽  
Author(s):  
Marco Montalva-Medel ◽  
Thomas Ledger ◽  
Gonzalo A. Ruz ◽  
Eric Goles
Keyword(s):  
Escherichia Coli ◽  
Limit Cycles ◽  
The Other ◽  
Lac Operon ◽  
Boolean Models ◽  
Bistable Behavior

In Veliz-Cuba and Stigler 2011, Boolean models were proposed for the lac operon in Escherichia coli capable of reproducing the operon being OFF, ON and bistable for three (low, medium and high) and two (low and high) parameters, representing the concentration ranges of lactose and glucose, respectively. Of these 6 possible combinations of parameters, 5 produce results that match with the biological experiments of Ozbudak et al., 2004. In the remaining one, the models predict the operon being OFF while biological experiments show a bistable behavior. In this paper, we first explore the robustness of two such models in the sense of how much its attractors change against any deterministic update schedule. We prove mathematically that, in cases where there is no bistability, all the dynamics in both models lack limit cycles while, when bistability appears, one model presents 30% of its dynamics with limit cycles while the other only 23%. Secondly, we propose two alternative improvements consisting of biologically supported modifications; one in which both models match with Ozbudak et al., 2004 in all 6 combinations of parameters and, the other one, where we increase the number of parameters to 9, matching in all these cases with the biological experiments of Ozbudak et al., 2004.

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