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31.
Differential spectrum of mutations that activate the Escherichia coli bgl operon in an rpoS genetic background 下载免费PDF全文
The bgl promoter is silent in wild-type Escherichia coli under standard laboratory conditions, and as a result, cells exhibit a beta-glucoside-negative (Bgl-) phenotype. Silencing is brought about by negative elements that flank the promoter and include DNA structural elements and sequences that interact with the nucleoid-associated protein H-NS. Mutations that confer a Bgl+ phenotype arise spontaneously at a detectable frequency. Transposition of DNA insertion elements within the regulatory locus, bglR, constitutes the major class of activating mutations identified in laboratory cultures. The rpoS-encoded sigmaS, the stationary-phase sigma factor, is involved in both physiological as well as genetic changes that occur in the cell under stationary-state conditions. In an attempt to see if the rpoS status of the cell influences the nature of the mutations that activate the bgl promoter, we analyzed spontaneously arising Bgl+ mutants in rpoS+ and rpoS genetic backgrounds. We show that the spectrum of activating mutations in rpoS cells is different from that in rpoS+ cells. Unlike rpoS+ cells, where insertions in bglR are the predominant activating mutations, mutations in hns make up the majority in rpoS cells. The physiological significance of these differences is discussed in the context of survival of natural populations of E. coli. 相似文献
32.
Hongyan Zheng Alina Beliavsky Anatoli Tchigvintsev Joseph S. Brunzelle Greg Brown Robert Flick Elena Evdokimova Zdzislaw Wawrzak Radhakrishnan Mahadevan Wayne F. Anderson Alexei Savchenko Alexander F. Yakunin 《Proteins》2013,81(6):1031-1041
Aldehyde dehydrogenases are found in all organisms and play an important role in the metabolic conversion and detoxification of endogenous and exogenous aldehydes. Genomes of many organisms including Escherichia coli and Salmonella typhimurium encode two succinate semialdehyde dehydrogenases with low sequence similarity and different cofactor preference (YneI and GabD). Here, we present the crystal structure and biochemical characterization of the NAD(P)+‐dependent succinate semialdehyde dehydrogenase YneI from S. typhimurium. This enzyme shows high activity and affinity toward succinate semialdehyde and exhibits substrate inhibition at concentrations of SSA higher than 0.1 mM. YneI can use both NAD+ and NADP+ as cofactors, although affinity to NAD+ is 10 times higher. High resolution crystal structures of YneI were solved in a free state (1.85 Å) and in complex with NAD+ (1.90 Å) revealing a two domain protein with the active site located in the interdomain interface. The NAD+ molecule is bound in the long channel with its nicotinamide ring positioned close to the side chain of the catalytic Cys268. Site‐directed mutagenesis demonstrated that this residue, as well as the conserved Trp136, Glu365, and Asp426 are important for activity of YneI, and that the conserved Lys160 contributes to the enzyme preference to NAD+. Our work has provided further insight into the molecular mechanisms of substrate selectivity and activity of succinate semialdehyde dehydrogenases. © 2012 Wiley Periodicals, Inc. 相似文献
33.
Raúl J. Gazmuri Kasen Whitehouse Karla Whittinghill Alvin Baetiong Jeejabai Radhakrishnan 《PloS one》2015,10(6)
Introduction
Current management of hemorrhagic shock (HS) in the battlefield and civilian settings favors small-volume fluid resuscitation before controlling the source of bleeding. We investigated in a swine model of HS the effects of vasopressin infusion along with small-volume fluid resuscitation; with erythropoietin (EPO) and HS severity as additional factors.Methods
HS was induced in 24 male domestic pigs (36 to 41 kg) by blood withdrawal (BW) through a right atrial cannula modeling spontaneous bleeding by a mono-exponential decay function. The initial 12 pigs received no fluids; the last 12 pigs received normal saline (NS) half the BW volume. Pigs were randomized 2:1 to receive intraosseously vasopressin (0.04 U/kg·min-1) or vehicle control from minute 7 to minute 210. Pigs assigned to vasopressin were further randomized 1:1 to receive EPO (1,200 U/kg) or vehicle control and 1:1 to have 65% or 75% BW of their blood volume. Shed blood was reinfused at 210 minutes and the pigs recovered from anesthesia.Results
Survival at 72 hours was influenced by vasopressin and NS but not by EPO or % BW. Vasopressin with NS promoted the highest survival (8/8) followed by vasopressin without NS (3/8), NS without vasopressin (1/4), and neither treatment (0/4) with overall statistical significance (log-rank test, p = 0.009) and each subset different from vasopressin with NS by Holm-Sidak test. Vasopressin increased systemic vascular resistance whereas NS increased cardiac output.Conclusion
Vasopressin infusion with small-volume fluid resuscitation during severe HS was highly effective enabling critical hemodynamic stabilization and improved 72 hour survival. 相似文献34.
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37.
Effect of trypsin, phospholipases, and membrane-impermeable reagents on the uptake of palmitic acid by isolated rat liver cells 总被引:7,自引:0,他引:7
Rat liver cells isolated by the collagenase-hyaluronidase perfusion method were treated with membrane-impermeable protein reagents (7-diazonium, 1–3-naphthalene disulfonate, diazotized sulfanilic acid, 8-anilino-naphthalene disulfonate), trypsin, phospholipase A, phospholipase C, and phospholipase D. The treated cells were incubated with [1-14C]palmitate and the 14CO2 produced was taken as a measure of fatty acid uptake by the cells. 14CO2 production by the cells was not inhibited after treatments with the membrane-impermeable protein reagents or phospholipase D. Treatments with small amounts of trypsin or phospholipases A or C caused inhibition of CO2 production from tracer amounts of palmitate. The inhibition by trypsin was partially, and that by phospholipase A was fully, reversed by increasing the amount of palmitic acid in the incubation medium. The oxidation of shorter-chain fatty acids such as octanoic acid was not decreased but increased after treating the cells with trypsin or phospholipase A. The membrane-impermeable reagents inhibited the oxidation of palmitate to CO2 by liver cells isolated by mechanical dispersion. These reagents also inhibited the long-chain acyl CoA ligase activity of liver microsomes. From these results it is suggested that the inhibition of CO2 production by intact liver cells from palmitate after enzyme treatments, is due to partial removal or modification of a normal transport component for long-chain fatty acids on the plasma membrane. The possibility of proteins (or lipoproteins) buried below the surface layer of plasma membrane in fatty acid uptake by liver cells is indicated. 相似文献
38.
Karthik Sivaraman Aditi Chopra Aparna Narayana Raghu A. Radhakrishnan 《Gerodontology》2021,38(1):17-26
Severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) is an RNA virus that causes coronavirus infection (COVID‐19). COVID‐19 is a highly contagious disease transmitted through respiratory droplets, saliva and other contact routes. Within 10 months of its outbreak, SARS‐CoV‐2 has infected more than 23 million people around the world. Evidence suggests that older adults are the most vulnerable to infection and have an increased risk of mortality. Reduced immunity and underlying medical conditions make them risk‐prone and vulnerable to critical care. Older adults affected with the SARS‐CoV‐2 virus present with distinct clinical manifestations necessitating specific treatment needs and management protocols. While it is crucial to prevent the spread of novel coronavirus (2019‐nCoV), the role of oral healthcare workers in addressing the specific needs of ageing adult patients by adopting specific guidelines and appropriate infection control protocols is timely. This paper aims to develop specific guidelines and protocols for the dental management of geriatric patients during the COVID‐19 pandemic. 相似文献
39.
Leaf blight disease of rice (Oryza sativa) is caused by the bacterium Xanthomonas oryzae pv. oryzae. Phenol (1 to 4 mM) induced changes in protein profiles of X. o. pv. oryzae and a stress protein with a molecular mass of 69,000 appeared. HPLC analysis indicated occurrence of amino acids such as asparagine, alanine, methionine and cystine in phenol treated cells. Proton NMR analysis also revealed variation on the presence of amino acids in the cells treated with phenol. 相似文献
40.
Shashank R. Joshi Ranjit Mohan Anjana Mohan Deepa Rajendra Pradeepa Anil Bhansali Vinay K. Dhandania Prashant P. Joshi Ranjit Unnikrishnan Elangovan Nirmal Radhakrishnan Subashini Sri Venkata Madhu Paturi Vishnupriya Rao Ashok Kumar Das Tanvir Kaur Deepak Kumar Shukla Viswanathan Mohan for the ICMR– INDIAB Collaborative Study Group 《PloS one》2014,9(5)