Formation of the nitrogen-fixing enzyme system in Azotobacter vinelandii

1968 ◽  
Vol 14 (1) ◽  
pp. 25-31 ◽  
Author(s):  
G. W. Strandberg ◽  
P. W. Wilson
Keyword(s):  
Color Change ◽  
Azotobacter Vinelandii ◽  
Nitrogenase Activity ◽  
Color Difference ◽  
Potassium Nitrate ◽  
Whole Cells ◽  
System A ◽  
Growth System ◽  
A Cell ◽  
Enzyme Formation

The formation and activity of nitrogenase2 in Azotobacter vinelandii OP was examined using a cell-free assay system. A lag period of about 30 min occurred between the exhaustion of the combined nitrogen source and growth on N2. Cells grown on ammonium acetate or potassium nitrate had no detectable nitrogenase activity. Nitrogenase activity appeared in cells, grown under a flowing gas phase of 20% O2 – 60% He, about 45 min after the exhaustion of ammonia. Nitrogenase formation was inhibited in a closed system with an atmosphere containing 40% O2 but not by one containing 20% O2. Hydrogen did not inhibit enzyme formation. The question of whether N2 is required for the formation of the enzyme could not be answered as this gas could not be completely eliminated from the growth system. Chloramphenicol prevented the formation of the enzyme and inhibited nitrogen fixation in whole cells, but had no effect on cell-free enzyme activity. A brief rise in turbidity which occurred during nitrogenase formation appeared to be due to a color change in the cells from reddish brown to dark brown. Spectrophotometric examination of extracts from ammonia- and N2-grown cells did not reveal any components responsible for this color difference, but this result may reflect only the presence of interfering substances in the crude extract.

Nitrogen fixation by cell-free extracts of Klebsiella pneumoniae

1968 ◽  
Vol 14 (1) ◽  
pp. 33-38 ◽  
Author(s):  
M. C. Mahl ◽  
P. W. Wilson
Keyword(s):  
Nitrogen Fixation ◽  
Klebsiella Pneumoniae ◽  
Azotobacter Vinelandii ◽  
Ammonium Ion ◽  
Michaelis Constant ◽  
Nitrogen Gas ◽  
Aerobacter Aerogenes ◽  
Free System ◽  
Evolving System ◽  
A Cell

A cell-free system which permits nitrogen fixation by extracts of Klebsiella pneumoniae M5al (formerly Aerobacter aerogenes) has been developed. It is, essentially, that system described by Bulen and associates for Azotobacter vinelandii, utilizing ATP as a source of energy and dithionite as a source of electrons. The Michaelis constant for fixation has been estimated to be 0.12 atm. The extracts possessed an ATP-dependent hydrogen evolving system. Hydrogen evolution from these extracts was less under nitrogen than under helium in the presence of ATP. Nitrogen gas appears to be the inducer of nitrogen fixation. In the absence of N2, no induction of nitrogenase occurs. Nitrogenase is absent in cells grown on NH4+-N. There is a lag of about 13 h after the introduction of N2 gas into a culture which has depleted its supply of NH4+-N before nitrogenase can be detected. For reasons discussed in the text, this conclusion must be regarded as tentative at this time. Ammonium ion appears to prevent the synthesis of new molecules of nitrogenase without affecting the activity of those already formed.

Optimal conditions for induction of competence in nitrogen-fixing Azotobacter vinelandii

1982 ◽  
Vol 28 (4) ◽  
pp. 389-397 ◽  
Author(s):  
William J. Page
Keyword(s):  
Dissolved Oxygen ◽  
Sodium Acetate ◽  
Azotobacter Vinelandii ◽  
Nitrogenase Activity ◽  
Cell Mass ◽  
Apparent Competition ◽  
Competence Development ◽  
Optimal Conditions ◽  
Nitrogen Fixing ◽  
Ph Range

Competence development in nitrogen-fixing Azotobacter vinelandii cells was optimal at pH 7.2–7.4 which necessitated additional buffering of the iron-limited nitrogen-free competence medium or the addition of a suitable organic acid salt, e.g., sodium acetate. An autolysin was active in this pH range and competent cells were more susceptible to autolysis than the general cell population. Competence development also required restricted aeration of the culture, and only those cultures that attained zero dissolved oxygen became competent. Restricted aeration served to protect the iron-limited cell nitrogenase from oxygen inactivation thus allowing the culture to reach zero dissolved oxygen. The inclusion of additional sources of reductant, e.g., malate, in buffered competence medium resulted in increased respiration and protection of nitrogenase, increased cell mass, and poly-β-hydroxybutyrate synthesis, but decreased competence. A possible explanation for the apparent competition between competence development and nitrogenase activity is discussed.

scholarly journals Cucurbitacins are insect steroid hormone antagonists acting at the ecdysteroid receptor

1997 ◽  
Vol 327 (3) ◽  
pp. 643-650 ◽  
Author(s):  
Laurence DINAN ◽  
Pensri WHITING ◽  
Jean-Pierre GIRAULT ◽  
René LAFONT ◽  
S. Tarlochan DHADIALLA ◽  
...  
Keyword(s):  
Morphological Changes ◽  
Antagonistic Activity ◽  
Side Chain ◽  
Ecdysteroid Receptor ◽  
Whole Cells ◽  
Definitive Evidence ◽  
Permanent Cell ◽  
A Cell ◽  
Gel Shift Assay ◽  
Hormone Antagonists

Two triterpenoids, cucurbitacins B and D, have been isolated from seeds of Iberis umbellata (Cruciferae) and shown to be responsible for the antagonistic activity of a methanolic extract of this species in preventing the 20-hydroxyecdysone (20E)-induced morphological changes in the Drosophila melanogaster BII permanent cell line. With a 20E concentration of 50 nM, cucurbitacins B and D give 50% responses at 1.5 and 10 μM respectively. Both cucurbitacins are able to displace specifically bound radiolabelled 25-deoxy-20-hydroxyecdysone (ponasterone A) from a cell-free preparation of the BII cells containing ecdysteroid receptors. The Kd values for cucurbitacins B and D (5 and 50 μM respectively) are similar to the concentrations required to antagonize 20E activity with whole cells. Cucurbitacin B (cucB) prevents stimulation by 20E of an ecdysteroid-responsive reporter gene in a transfection assay. CucB also prevents the formation of the Drosophila ecdysteroid receptor/Ultraspiracle/20E complex with the hsp27 ecdysteroid response element as demonstrated by gel-shift assay. This is therefore the first definitive evidence for the existence of antagonists acting at the ecdysteroid receptor. Preliminary structure/activity studies indicate the importance of the Δ23-22-oxo functional grouping in the side chain for antagonistic activity. Hexanorcucurbitacin D, which lacks carbon atoms C-22 to C-27, is found to be a weak agonist rather than an antagonist. Moreover, the side chain analogue 5-methylhex-3-en-2-one possesses weak antagonistic activity.

scholarly journals Influence of UV Radiation on the Color Change of the Surface of Steamed Maple Wood with Saturated Water Steam

Polymers ◽  
2022 ◽  
Vol 14 (1) ◽  
pp. 217
Author(s):  
Ladislav Dzurenda ◽  
Michal Dudiak ◽  
Eva Výbohová
Keyword(s):  
Uv Radiation ◽  
Color Change ◽  
Color Space ◽  
Color Stability ◽  
Color Difference ◽  
Saturated Steam ◽  
Water Steam ◽  
Saturated Water ◽  
Red Color ◽  
Uv Lamp

The wood of maple (Acer Pseudopatanus L.) was steamed with a saturated steam-air mixture at a temperature of t = 95 °C or saturated steam at t = 115 °C and t = 135 °C, in order to give a pale pink-brown, pale brown, and brown-red color. Subsequently, samples of unsteamed and steamed maple wood were irradiated with a UV lamp in a Xenotest Q-SUN Xe-3-H after drying, in order to test the color stability of steamed maple wood. The color change of the wood surface was evaluated by means of measured values on the coordinates of the color space CIE L* a* b*. The results show that the surface of unsteamed maple wood changes color markedly under the influence of UV radiation than the surface of steamed maple wood. The greater the darkening and browning color of the maple wood by steaming, the smaller the changes in the values at the coordinates L*, a*, b* of the steamed maple wood caused by UV radiation. The positive effect of steaming on UV resistance is evidenced by the decrease in the overall color difference ∆E*. While the value of the total color diffusion of unsteamed maple wood induced by UV radiation is ∆E* = 18.5, for maple wood steamed with a saturated steam-air mixture at temperature t = 95 °C the ∆E* decreases to 12.6, for steamed maple wood with saturated water steam with temperature t = 115 °C the ∆E* decreases to 10.4, and for saturated water steam with temperature t = 135 °C the ∆E* decreases to 7.2. Differential ATR-FTIR spectra declare the effect of UV radiation on unsteamed and steamed maple wood and confirm the higher color stability of steamed maple wood.

scholarly journals PENGARUH RESIN TERHADAP PERUBAHAN WARNA PADA CAT TEMBOK

2019 ◽  
Vol 5 (2) ◽  
pp. 132
Author(s):  
Nurlela Nurlela ◽  
Risnawati Risnawati
Keyword(s):  
Film Thickness ◽  
Vinyl Acetate ◽  
Polyvinyl Acetate ◽  
Color Change ◽  
Color Difference ◽  
Background Color ◽  
Color Changes ◽  
Synthetic Resins ◽  
Color Background

The Influence of Resin against the Change of Color on the Wall PaintThe quality of the paint is determined by the resin used. Synthetic resins for polymer paints are made by combining several monomers to achieve various characteristics. The incorporation of some monomers such as polyvinyl acetate resin, acrylic vinyl resin and acrylic styrene resin which act as a binder can affect the quality of the paint especially the color change. The purpose of this study is to find the color changes that occur on the wall paint by using Poly Styrene Acrylic , Poly Vinyl Acetate and Poly Vinyl Acrylic. From the results of the measurement of color difference, significant color change occurs in the Poly Vinyl Acetate (PVAc) + Poly Vinyl Acrylic (PVA) and Poly Styrene Acrylic (PSA). The results of the quality test of the three resins based on pH test, scrub test and viscosity test, PSA has better quality compared to PVA + PVAc and PVA resin. From the color difference measurement test, some things need to be considered, are temperature, film thickness, substrate color/background color and measurement conditions (measured in wet sample/in plate/dry surface) and test on resin added additive according to the type of each resin.Keywords: Paint, Resin, Color Changes, Poly Vinyl Acetate, Poly Styrene.ABSTRAK Kualitas dari cat sangat ditentukan oleh resin yang digunakan. Resin sintetis untuk cat berupa polimer yang dibuat dengan menggabung beberapa monomer untuk mencapai berbagai karakteristik. Penggabungan dari beberapa monomer seperti resin poli vinil asetat, resin vinil akrilik dan resin stirena akrilik yang berfungsi sebagai pengikat mampu mempengaruhi kualitas cat terutama dari perubahan warna. Tujuan dari penelitian ini adalah untuk mengetahui perubahan warna yang terjadi pada cat tembok dengan menggunakan Poli Stirena Akrilik, Poli Vinil asetat dan Poli Vinil Akrilik. Dari hasil pengukuran perbedaan warna, perubahan warna cukup signifikan terjadi pada resin Poli vinil Asetat (PVAc) + Poli Vinil Akrilik (PVA) dan resin  Poli Stirena Akrilik (PSA). Hasil uji Kualitas cat dari ketiga resin berdasarkan uji pH, uji scrub dan uji viscositas, PSA memiliki kualitas yang lebih baik dibandingkan dengan resin PVA+PVAc dan PVA. Dari pengujian pengukuran perbedaan warna, beberapa hal yang perlu di perhatikan, yaitu suhu, film thickness, warna substrat/background color dan kondisi pengukuran (diukur dalam keadaan wet sample/dalam bentuk plate/dry surface) dan pengujian terhadap resin yang ditambahkan zat aditif yang sesuai dengan tipe masing-masing resin tersebut.Kata Kunci: Cat, Resin, Perubahan Warna, Poli Vinil, Poli Stirena.

scholarly journals SCREENING OF SOIL BACTERIA FOR PLANT GROWTH PROMOTION ACTIVITIES IN VITRO

2016 ◽  
Vol 4 (1) ◽  
pp. 27 ◽  
Author(s):  
Edi Husen
Keyword(s):  
Plant Growth ◽  
Soil Bacteria ◽  
Phosphate Solubilization ◽  
Azotobacter Vinelandii ◽  
Growth Promotion ◽  
Nitrogenase Activity ◽  
Chelating Agent ◽  
Plant Growth Promoting Rhizobacteria ◽  
Iaa Production

Fourteen isolates of soil bacteria, including two known plant growth promoting rhizobacteria (PGPR) strains, Azotobacter vinelandii Mac 259 and Bacillus cereus UW 85, were tested in vitro. Parameters assessed were indoleacetic acid (IAA) production, phosphate solubilization, dinitrogen fixation, and siderophore (Fe-III chelating agent) production. IAA production was assayed colorimetrically using ferric chlorideperchloric acid reagent. Phosphate-solubilization and siderophore production were tested qualitatively by plating the bacteria in Pikovskaya and chrome azurol S agar, respectively. The ability to fix dinitrogen was measured based on nitrogenase activity of the bacteria by gas chromatography. The results showed that twelve isolates produced IAA, ranged from 2.09 to 33.28 µmol ml-1. The ability to solubilize precipitated phosphate was positively exhibited by four isolates (BS 58, BTS, TCaR 61, and BTCaRe 65). Seven isolates including Mac 259 positively produced siderophore. None of the isolates showed nitrogenase activity. Only one isolate (TS 3) did not exhibit any of the traits tested. Isolate TCeRe 60 and reference strain Mac 259 were found to have IAA- and siderophore-producing traits. Four P-solubilizing bacteria (BS 58, BTS, TCaR 61, and BTCaRe 65) were also IAA- and siderophore-producing bacteria. Potential use of these PGPR isolates needs further test in enhancing plant growth.

How penicillin kills bacteria: progress and problems

1971 ◽  
Vol 179 (1057) ◽  
pp. 369-383 ◽  
Keyword(s):  
Staphylococcus Aureus ◽  
Cell Wall ◽  
Bacterial Cell ◽  
Crosslinking Reaction ◽  
Free System ◽  
Whole Cells ◽  
Uridine Nucleotide ◽  
History Of ◽  
A Cell ◽  
Specific Inhibitors

Penicillins and cephalosporins are specific inhibitors of the biosynthesis of bacterial cell walls. This discovery was first made in 1957 and was based on two observations. First, penicillins induced the formation of protoplasts or spheroplasts in bacteria (organisms in which the cell wall has been lost or weakened) (Lederberg 1957). Secondly, a uridine nucleotide accumulated in Staphylococcus aureus and other bacteria inhibited by penicillin which had a striking relationship to the composition of the cell wall (Park & Strominger 1957). It was therefore suggested that this nucleotide was an activated precursor of the wall. Over the next decade, a great deal of work was carried out in order to elucidate the structure of the bacterial cell wall and the mechanism of its biosynthesis from the uridine nucleotides and other precursors (reviewed by Strominger 1970; Strominger & Ghuysen 1967; Ghuysen 1968). It was demonstrated that interpeptide cross-links were an important structural feature of the wall. Several kinds of experiments carried out with whole cells indicated that the final step in cell wall synthesis, the crosslinking reaction catalysed by a transpeptidase, was the site of action of penicillin (Wise & Park 1965; Tipper & Strominger 1965 a , b , 1968). Finally, in 1966, the transpeptidase catalysing this cross-linking reaction was obtained in a cell-free system and shown to be a penicillin-sensitive enzyme (Izaki, Matsuhashi & Strominger 1966, 1968). The history of these developments has been reviewed elsewhere (Strominger 1970), and in the present paper, attention will be focused on recent studies of the penicillin-sensitive transpeptidase and other penicillinsensitive activities found in bacterial cell membranes. First, however, it is necessary to describe briefly the structure of the cell wall of bacteria and the nature of the inhibited reactions. The walls of bacteria consist of glycan strands in which two sugars, acetylglucosamine (X) and acetylmuramic acid (Y), strictly alternate (figure 1). Four such glycan strands are represented in figure 1. The acetylmuramic acid residues of the polymer are substituted by a tetrapeptide (represented in the figure by open circles). The peptidoglycan strand (i.e., the glycan substituted by the tetrapeptide) are cross-linked to one another by means of an interpeptide bridge which is to some extent a genus-specific character­istic. In the genus Staphylococcus aureus , the interpeptide bridge is a pentaglycine chain (represented in figure 1 by the closed circles) which extends from the carboxyl group on the terminal D-alanine residue of the tetrapeptide to the ∊-amino group of lysine, the third amino acid in the tetrapeptide chain. The wall of S . aureus is a very tightly knit structure in that virtually every peptide subunit is cross-linked to another subunit by means of this interpeptide bridge. Penicillins and cephalosporins are specific inhibitors of the reaction in which the cross-link is actually formed. This step is the last reaction in wall synthesis.

Sign in / Sign up

Export Citation Format

Share Document