scholarly journals The steady-state kinetics of the NADH-dependent nitrite reductase from Escherichia coli K 12. Nitrite and hydroxylamine reduction

1981 ◽  
Vol 199 (1) ◽  
pp. 171-178 ◽  
Author(s):  
R H Jackson ◽  
J A Cole ◽  
A Cornish-Bowden
Keyword(s):  
Escherichia Coli ◽  
Nitrite Reductase ◽  
Substrate Inhibition ◽  
Maximum Velocity ◽  
Product Inhibition ◽  
Mixed Product ◽  
Enzyme Form ◽  
Wide Range ◽  
No2 Reduction ◽  
K 12

The reduction of both NO2- and hydroxylamine by the NADH-dependent nitrite reductase of Escherichia coli K 12 (EC 1.6.6.4) appears to follow Michaelis-Menten kinetics over a wide range of NADH concentrations. Substrate inhibition can, however, be detected at low concentrations of the product NAD+. In addition, NAD+ displays mixed product inhibition with respect to NADH and mixed or uncompetitive inhibition with respect to hydroxylamine. These inhibition characteristics are consistent with a mechanism in which hydroxylamine binds during catalysis to a different enzyme form from that generated when NAD+ is released. The apparent maximum velocity with NADH as varied substrate increases as the NAD+ concentration increases from 0.05 to 0.7 mM with 1 mM-NO2- or 100 mM-hydroxylamine as oxidized substrate. This increase is more marked for hydroxylamine reduction than for NO2- reduction. Models incorporating only one binding site for NAD can account for the variation in the Michaelis-Menten parameters for both NADH and hydroxylamine with [NAD+] for hydroxylamine reduction. According to these models, activation of the reaction occurs by reversal of an over-reduction of the enzyme by NADH. If the observed activation of the enzyme by NAD+ derives both from activation of the generation of the enzyme-hydroxylamine complex from the enzyme-NO2- complex during NO2- reduction and from activation of the reduction of the enzyme-hydroxylamine complex to form NH4+, then the variation of Vapp. for NO2- or hydroxylamine with [NAD+] is consistent with the occurrence of the same enzyme-hydroxylamine complex as an intermediate in both reactions.

scholarly journals Bioinformatic and Molecular Analysis of Inverse Autotransporters from Escherichia coli

mSphere ◽  
2019 ◽  
Vol 4 (4) ◽  
Author(s):  
Kelvin G. K. Goh ◽  
Danilo G. Moriel ◽  
Steven J. Hancock ◽  
Minh-Duy Phan ◽  
Mark A. Schembri
Keyword(s):  
Escherichia Coli ◽  
Cell Surface ◽  
Biofilm Formation ◽  
Secretion System ◽  
Content Type ◽  
E Coli ◽  
Wide Range ◽  
Type V Secretion ◽  
K 12 ◽  
Type V

ABSTRACT Proteins secreted by the type V secretion system possess multiple functions, including the capacity to mediate adhesion, aggregation, and biolfilm formation. The type V secretion system can be divided into five subclasses, one of which is the type Ve system. Proteins of the type Ve secretion system are also referred to as inverse autotransporters (IATs). In this study, we performed an in silico analysis of 126 completely sequenced Escherichia coli genomes available in the NCBI database and identified several distinct IAT-encoding gene families whose distribution varied throughout the E. coli phylogeny. The genes included three characterized IATs (intimin, fdeC, and yeeJ) and four uncharacterized IATs (here named iatA, iatB, iatC, and iatD). The four iat genes were cloned from the completely sequenced environmental E. coli strain SMS-3-5 and characterized. Three of these IAT proteins (IatB, IatC, and IatD) were expressed at the cell surface and possessed the capacity to mediate biofilm formation in a recombinant E. coli K-12 strain. Further analysis of the iatB gene, which showed a unique association with extraintestinal E. coli strains, suggested that its regulation is controlled by the LeuO global regulator. Overall, this study provides new data describing the prevalence, sequence variation, domain structure, function, and regulation of IATs found in E. coli. IMPORTANCE Escherichia coli is one of the most prevalent facultative anaerobes of the human gut. E. coli normally exists as a harmless commensal but can also cause disease following the acquisition of genes that enhance its pathogenicity. Adhesion is an important first step in colonization of the host and is mediated by an array of cell surface components. In E. coli, these include a family of adhesins secreted by the type V secretion system. Here, we identified and characterized new proteins from an emerging subclass of the type V secretion system known as the inverse autotransporters (IATs). We found that IAT-encoding genes are present in a wide range of strains and showed that three novel IATs were localized on the E. coli cell surface and mediated biofilm formation. Overall, this study provides new insight into the prevalence, function, and regulation of IATs in E. coli.

scholarly journals The steady state kinetics of the NADH-dependent nitrite reductase from Escherichia coli K12. The reduction of single-electron acceptors

1982 ◽  
Vol 203 (2) ◽  
pp. 505-510 ◽  
Author(s):  
R H Jackson ◽  
J A Cole ◽  
A Cornish-Bowden
Keyword(s):  
Escherichia Coli ◽  
Cytochrome C ◽  
Nitrite Reductase ◽  
Maximum Velocity ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Steady State Kinetics ◽  
Cytochrome C Reduction ◽  
Pattern Of Variation ◽  
Rate Limiting

The kinetic characteristics of the diaphorase activities associated with the NADH-dependent nitrite reductase (EC 1.6.6.4) from Escherichia coli have been determined. The values of the apparent maximum velocity are similar for the reduction of Fe(CN)6(3)-and mammalian cytochrome c by NADH. These reactions may therefore have the same rate-limiting step. NAD+ activates NADH-dependent reduction of cytochrome c, and the apparent maximum velocity for this substrate increases more sharply with the concentration of NAD+ than for hydroxylamine. The simplest explanation is that NAD+ activation of hydroxylamine reduction derives solely from activation of steps involved in the reduction of cytochrome c, a flavin-mediated reaction, but these steps are only partly rate-limiting for the reduction of hydroxylamine. At 0.5 mM-NAD+, the apparent maximum velocity was 2.3 times higher for 0.1 mM-cytochrome c as substrate than for 100 mM-hydroxylamine, suggesting that the rate-limiting step during hydroxylamine reduction is a step that is not involved in cytochrome c reduction. A scheme is proposed that can account for the pattern of variation with [NAD+] of the Michaelis-Menten parameters for hydroxylamine and for NADH with hydroxylamine or cytochrome c as oxidized substrate.

scholarly journals Lipopolysaccharide core type diversity in the Escherichia coli species in association with phylogeny, virulence gene repertoire and distribution of type VI secretion systems

2021 ◽  
Vol 7 (9) ◽  
Author(s):  
Sébastien O. Leclercq ◽  
Maxime Branger ◽  
David G. E. Smith ◽  
Pierre Germon
Keyword(s):  
Escherichia Coli ◽  
Type Species ◽  
Virulence Gene ◽  
Uneven Distribution ◽  
Gene Repertoire ◽  
Content Type ◽  
E Coli ◽  
Link Type ◽  
Wide Range ◽  
K 12

Escherichia coli is a very versatile species for which diversity has been explored from various perspectives highlighting, for example, phylogenetic groupings and pathovars, as well as a wide range of O serotypes. The highly variable O-antigen, the most external part of the lipopolysaccharide (LPS) component of the outer membrane of E. coli , is linked to the innermost lipid A through the core region of LPS of which five different structures, denominated K-12, R1, R2, R3 and R4, have been characterized so far. The aim of the present study was to analyse the prevalence of these LPS core types in the E. coli species and explore their distribution in the different E. coli phylogenetic groups and in relationship with the virulence gene repertoire. Results indicated an uneven distribution of core types between the different phylogroups, with phylogroup A strains being the most diverse in terms of LPS core types, while phylogroups B1, D and E strains were dominated by the R3 type, and phylogroups B2 and C strains were dominated by the R1 type. Strains carrying the LEE virulence operon were mostly of the R3 type whatever the phylogroup while, within phylogroup B2, strains carrying a K-12 core all belonged to the complex STc131, one of the major clones of extraintestinal pathogenic E. coli (ExPEC) strains. The origin of this uneven distribution is discussed but remains to be fully explained, as well as the consequences of carrying a specific core type on the wider aspects of bacterial phenotype.

scholarly journals Alternative-substrate inhibition and the kinetic mechanism of the β-galactoside/proton symport of Escherichia coli

1982 ◽  
Vol 204 (3) ◽  
pp. 681-688 ◽  
Author(s):  
M G Page ◽  
Y H Jou
Keyword(s):  
Escherichia Coli ◽  
Substrate Concentration ◽  
Substrate Inhibition ◽  
Maximum Velocity ◽  
Kinetic Mechanism ◽  
Kinetic Constants ◽  
Alternative Substrate ◽  
Proton Binding ◽  
Alternative Substrates ◽  
Proton Symport

The effects of competing alternative substrates on the rate of uptake by galactoside/proton symport were investigated. These experiments produced a decrease in apparent maximum velocity with increased alternative-substrate concentration that cannot be accounted for by a simple ordered mechanism. This, together with non-linearities in the variation of the apparent kinetic constants with alternative-substrate concentration, can be accounted for by a random mechanism for galactoside and proton binding.

scholarly journals The NsrR Regulon of Escherichia coli K-12 Includes Genes Encoding the Hybrid Cluster Protein and the Periplasmic, Respiratory Nitrite Reductase

2007 ◽  
Vol 189 (12) ◽  
pp. 4410-4417 ◽  
Author(s):  
Nina Filenko ◽  
Stephen Spiro ◽  
Douglas F. Browning ◽  
Derrick Squire ◽  
Tim W. Overton ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Escherichia Coli ◽  
Nitrite Reductase ◽  
Reactive Nitrogen Species ◽  
Defense Mechanism ◽  
Regulatory Protein ◽  
Reactive Nitrogen ◽  
Nitrogen Species ◽  
Hybrid Cluster ◽  
K 12

ABSTRACT Successful pathogens must be able to protect themselves against reactive nitrogen species generated either as part of host defense mechanisms or as products of their own metabolism. The regulatory protein NsrR (a member of the Rrf2 family of transcription factors) plays key roles in this stress response. Microarray analysis revealed that NsrR represses nine operons encoding 20 genes in Escherichia coli MG1655, including the hmpA, ytfE, and ygbA genes that were previously shown to be regulated by NsrR. Novel NsrR targets revealed by this study include hcp-hcr (which were predicted in a recent bioinformatic study to be NsrR regulated) and the well-studied nrfA promoter that directs the expression of the periplasmic respiratory nitrite reductase. Conversely, transcription from the ydbC promoter is strongly activated by NsrR. Regulation of the nrf operon by NsrR is consistent with the ability of the periplasmic nitrite reductase to reduce nitric oxide and hence protect against reactive nitrogen species. Gel retardation assays were used to show that both FNR and NarL bind to the hcp promoter. The expression of hcp and the contiguous gene hcr is not induced by hydroxylamine. As hmpA and ytfE encode a nitric oxide reductase and a mechanism to repair iron-sulfur centers damaged by nitric oxide, the demonstration that hcp-hcr, hmpA, and ytfE are the three transcripts most tightly regulated by NsrR highlights the possibility that the hybrid cluster protein, HCP, might also be part of a defense mechanism against reactive nitrogen stress.

scholarly journals 3-Hydroxy-3-methylglutaryl-coenzyme A synthase from ox liver. Purification, molecular and catalytic properties

1985 ◽  
Vol 227 (2) ◽  
pp. 591-599 ◽  
Author(s):  
D M Lowe ◽  
P K Tubbs
Keyword(s):  
Coenzyme A ◽  
Catalytic Properties ◽  
Substrate Inhibition ◽  
Product Inhibition ◽  
Purification Procedure ◽  
Acetyl Coa ◽  
Mixed Product ◽  
Cellulose Phosphate ◽  
Ping Pong ◽  
Enzyme Intermediate

Mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase (EC 4.1.3.5) was purified to homogeneity from ox liver and obtained essentially free from acetoacetyl-CoA thiolase activity. The purification procedure included substrate elution from cellulose phosphate and chromatofocusing. The relative molecular mas was about 100 000 and S20,w0 was 6.36S. The enzyme appears to be a dimer of identical subunits (Mr 47 900). The Km for acetoacetyl-CoA is extremely low (less than 0.5 microM), and acetoacetyl-CoA (Acac-CoA) gives marked substrate inhibition (KiAcac-CoA = 3.5 microM) that is competitive with respect to acetyl-CoA. Both CoA and DL-3-hydroxy-3-methylglutaryl-CoA give mixed product inhibition with respect to acetyl-CoA, which is compatible with a Ping Pong mechanism in which both products can form kinetically significant complexes with two forms of the enzyme. The two forms are most likely to be free enzyme and an acetyl-enzyme intermediate.

LPS core type diversity in the Escherichia coli species and associations with phylogeny and virulence gene repertoire.

2021 ◽  
Author(s):  
Sebastien Olivier Leclercq ◽  
Maxime Branger ◽  
David GE Smith ◽  
Pierre GERMON
Keyword(s):  
Escherichia Coli ◽  
Lipid A ◽  
Virulence Gene ◽  
Uneven Distribution ◽  
Gene Repertoire ◽  
Phylogenetic Groups ◽  
E Coli ◽  
Wide Range ◽  
External Part ◽  
K 12

Escherichia coli is a very versatile species for which diversity has been explored from various perspectives highlighting, for example, phylogenetic groupings, pathovars as well as a wide range of O serotypes. The highly variable O-antigen, the most external part of the lipopolysaccharide component of the outer membrane of E. coli, is linked to the innermost lipid A through the core region of LPS of which 5 different structures, denominated K-12, R1, R2, R3 and R4, have been characterized so far. The aim of the present study was to analyze the prevalence of these LPS core types in the E. coli species and explore their distribution in the different E. coli phylogenetic groups and in relationship with the virulence gene repertoire. Results indicated an uneven distribution of core types between the different phylogroups, with phylogroup A strains being the most diverse in terms of LPS core types while phylogroups B1, D and E strains were dominated by the R3 type and phylogroups B2 and C strains being dominated by the R1 type. Strains carrying the LEE virulence operon were mostly of the R3 type whatever the phylogroup while, within phylogroup B2, strains carrying a K-12 core all belonged to the complex STc131, one of the major clone of extra-intestinal pathogenic E. coli(ExPEC) strains. The origin of this uneven distribution is discussed but remains to be explained, as well as the consequences of carrying a specific core type on the physiology of the bacteria.

END-PRODUCT INHIBITION OF THREONINE DEAMINASE OF STREPTOMYCIN MUTANTS OF ESCHERICHIA COLI K-12

1967 ◽  
Vol 45 (1) ◽  
pp. 11-18 ◽  
Author(s):  
I. D. Desai ◽  
W. J. Polglase
Keyword(s):  
Escherichia Coli ◽  
Feedback Regulation ◽  
Product Inhibition ◽  
Threshold Concentration ◽  
Regulatory Function ◽  
Wild Type ◽  
Threonine Deaminase ◽  
Structural Differences ◽  
Dependent Strain ◽  
K 12

In the presence of end product (L-isoleucine), the biosynthetic threonine deaminase in extracts of streptomycin mutants of Escherichia coli K-12 gave a sigmoid response to increasing substrate (L-threonine) concentration. The response to inhibitor at constant substrate concentration was similar. However, the mutants showed quantitative differences in the "threshold" concentration of effector (substrate or inhibitor) required to produce the response. The smallest threshold was observed with the wild-type (streptomycin-sensitive) strain and the largest threshold with the streptomycin-resistant (indifferent) strain. The streptomycin-dependent strain was intermediate. The differences in response to effector may be caused by structural differences at the sites of bonding between subunits of the enzyme protein.These observations on feedback regulation, together with previous observations on repression in streptomycin mutants, indicate that the effects of the antibiotic are directed towards enzymes which perform a regulatory function.

scholarly journals Adaptive Evolution of Escherichia coli K-12 MG1655 during Growth on a Nonnative Carbon Source, l-1,2-Propanediol

2010 ◽  
Vol 76 (13) ◽  
pp. 4158-4168 ◽  
Author(s):  
Dae-Hee Lee ◽  
Bernhard Ø. Palsson
Keyword(s):  
Escherichia Coli ◽  
Carbon Source ◽  
Adaptive Evolution ◽  
Evolutionary Biology ◽  
Microbial Evolution ◽  
E Coli ◽  
A Genome ◽  
Wide Range ◽  
Whole Genome Resequencing ◽  
K 12

ABSTRACT Laboratory adaptive evolution studies can provide key information to address a wide range of issues in evolutionary biology. Such studies have been limited thus far by the inability of workers to readily detect mutations in evolved microbial strains on a genome scale. This limitation has now been overcome by recently developed genome sequencing technology that allows workers to identify all accumulated mutations that appear during laboratory adaptive evolution. In this study, we evolved Escherichia coli K-12 MG1655 with a nonnative carbon source, l-1,2-propanediol (l-1,2-PDO), for ∼700 generations. We found that (i) experimental evolution of E. coli for ∼700 generations in 1,2-PDO-supplemented minimal medium resulted in acquisition of the ability to use l-1,2-PDO as a sole carbon and energy source so that the organism changed from an organism that did not grow at all initially to an organism that had a growth rate of 0.35 h−1; (ii) six mutations detected by whole-genome resequencing accumulated in the evolved E. coli mutant over the course of adaptive evolution on l-1,2-PDO; (iii) five of the six mutations were within coding regions, and IS5 was inserted between two fuc regulons; (iv) two major mutations (mutations in fucO and its promoter) involved in l-1,2-PDO catabolism appeared early during adaptive evolution; and (v) multiple defined knock-in mutant strains with all of the mutations had growth rates essentially matching that of the evolved strain. These results provide insight into the genetic basis underlying microbial evolution for growth on a nonnative substrate.

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