scholarly journals Purification and characterization of the inactive MoFe protein (NifB-Kp1) of the nitrogenase from nifB mutants of Klebsiella pneumoniae

1983 ◽  
Vol 209 (1) ◽  
pp. 43-50 ◽  
Author(s):  
T R Hawkes ◽  
B E Smith
Keyword(s):  
Klebsiella Pneumoniae ◽  
Double Mutant ◽  
Specific Activity ◽  
Equimolar Amount ◽  
Wild Type ◽  
Purification And Characterization ◽  
Point Mutant ◽  
Mofe Protein ◽  
Iron Molybdenum Cofactor

The inactive MoFe protein of nitrogenase, NifB-Kp1, from two distinct nifB mutants of Klebsiella pneumoniae, Kp5058 (a nifB point mutant) and UNF1718 (a nifB, nifJ double mutant) has been purified and characterized. NifB-Kp1 can be activated by reaction with the iron-molybdenum cofactor, FeMoco, extracted from active MoFe protein. NifB-Kp1 purified from either source had similar properties and was contaminated with an approximately equimolar amount of protein of mol.wt. 21 000. Like active wild-type Kp1, it was an alpha 2 beta 2 tetramer, but it was far less stable than Kp1, deteriorating rapidly at temperatures above 8 degrees C or on mild oxidation. NifB-Kp1 preparations contained 0.4-0.9 Mo and 9.0 +/- 0.9 Fe atoms . mol-1 and, when activated by FeMoco, had a specific activity of approx. 500 units . mg-1. The Mo in our preparations was not associated with the e.p.r. signal normally observed from FeMoco. All preparations exhibited a weak gav. = 1.95 e.p.r. signal which was probably not associated with activatable protein.

scholarly journals The inactive MoFe protein (NifB−Kp1) of the nitrogenase from nif B mutants of Klebsiella pneumoniae. Its interaction with FeMo-cofactor and the properties of the active MoFe protein formed

1984 ◽  
Vol 223 (3) ◽  
pp. 783-792 ◽  
Author(s):  
T R Hawkes ◽  
B E Smith
Keyword(s):  
Klebsiella Pneumoniae ◽  
Signal Intensity ◽  
Specific Activity ◽  
Maximum Activity ◽  
Gene Products ◽  
Wild Type ◽  
Activation Reaction ◽  
Mofe Protein ◽  
Femo Cofactor ◽  
Iron Molybdenum Cofactor

The inactive MoFe protein (NifB-Kp1) of nitrogenase from nifB mutants of Klebsiella pneumoniae may be activated by addition of the iron-molybdenum cofactor (FeMoco) extracted from active MoFe protein (Kp1). However, when apparently saturated with FeMoco, our preparations of NifB-Kp1 yielded activated protein, Kp1-asm, with a specific activity that was at best only 40% of that expected. This was not due to degradation of Kp1-asm, NifB-Kp1 or FeMoco during the activation reaction. Nor could activation be enhanced by addition of other nif-gene products or other proteins. Whereas fully active Kp1 contains 2 FeMoco/molecule, apparent saturation of our NifB-Kp1 preparations required the binding of only 0.4-0.65 FeMoco/molecule. By using chromatography Kp1-asm could be largely resolved from NifB-Kp1 that had not been activated. However, we were unable to isolate fully active MoFe protein (i.e. Kp1-asm containing 2 FeMoco/molecule) from solutions of NifB-Kp1 activated with FeMoco. The maximum activity/ng-atom of total Mo obtained for our purified Kp1-asm was approximately half the maximum activity for FeMoco. Since all NifB-Kp1 preparations contained some Mo, we suggest that FeMoco activated only those NifB-Kp1 molecules already containing one atom of (non-FeMoco) Mo, thus forming Kp1-asm with 2 Mo but only 1 FeMoco/molecule. Kp1-asm was identical with normal Kp1 in terms of its Mr, stability, e.p.r. signals, pattern of substrate reductions, CO inhibition and ATP/2e ratio. In addition, for preparations of differing specific activity, there was a constant and identical relationship between the e.p.r. signal intensity (from FeMoco) and the activity of both Kp1 and Kp1-asm. Assuming the above hypothesis on the structure of Kp1-asm, these data demonstrate that the two FeMoco sites in wild-type Kp1 operate independently.

scholarly journals Nitrogenase from nifV mutants of Klebsiella pneumoniae contains an altered form of the iron-molybdenum cofactor

1984 ◽  
Vol 217 (1) ◽  
pp. 317-321 ◽  
Author(s):  
T R Hawkes ◽  
P A McLean ◽  
B E Smith
Keyword(s):  
Klebsiella Pneumoniae ◽  
Active Site ◽  
Molybdenum Cofactor ◽  
Wild Type ◽  
H2 Evolution ◽  
Mofe Protein ◽  
Fe Protein ◽  
Metal Contents ◽  
Altered Form ◽  
Iron Molybdenum Cofactor

When the iron-molybdenum cofactor (FeMoco) was extracted from the MoFe protein of nitrogenase from a nifV mutant of Klebsiella pneumoniae and combined with the FeMoco-deficient MoFe protein from a nifB mutant, the resultant MoFe protein exhibited the NifV phenotype, i.e. in combination with wild-type Fe protein it exhibited poor N2-fixation activity and its H2-evolution activity was inhibited by CO. These data provide strong evidence that FeMoco contains the active site of nitrogenase. The metal contents and e.p.r. properties of FeMoco from wild-type and nifV mutants of K. pneumoniae are very similar.

scholarly journals Klebsiella pneumoniae nitrogenase MoFe protein: chymotryptic proteolysis affects function by limited cleavage of the β-chain and provides high-specific-activity MoFe protein

1993 ◽  
Vol 291 (1) ◽  
pp. 309-314
Author(s):  
K Fisher ◽  
D J Lower ◽  
R N Pau
Keyword(s):  
Klebsiella Pneumoniae ◽  
Specific Activity ◽  
Gel Filtration ◽  
High Specific Activity ◽  
Visible Spectrum ◽  
Prolonged Treatment ◽  
Beta Chain ◽  
Wild Type ◽  
Alpha Chain ◽  
Mofe Protein

Proteinase treatment with chymotrypsin has been used to probe the structure of native Klebsiella pneumoniae nitrogenase MoFe protein (Kp1). Reaction with chymotrypsin did not bleach Kp1, suggesting that it did not destroy the metal centres, and the Mo and Fe contents of Kp1 were unchanged. High ratios of chymotrypsin to Kp1 (1:1 by mass) cleaved the beta-chain of Kp1 to give 44 and 14 kDa polypeptides, which N-terminal amino acid sequence analysis showed to be derived from cleavage at residue beta-Phe124. A mutant MoFe protein, Kp1Met-124, in which beta-Phe124 is replaced by methionine, was not cleaved by chymotrypsin. Under non-denaturing conditions, the ‘nicked’ beta-chain of the wild-type protein remained associated with the alpha-chain. The alpha-chain was not cleaved by the proteinase treatment. Fission of the wild-type beta-chain was accompanied by loss of enzyme activity, loss of intensity of the g = 3.7 e.p.r. signal derived from dithionite-reduced FeMoco and by changes in the visible spectrum. The e.p.r. spectra of potassium ferricyanide-oxidized native and digested Kp1 show differences in the signals between g = 1.6 and 2.0. After prolonged treatment, the final specific activity of Kp1 was about 25 +/- 5% of the initial activity. This corresponded to 25 +/- 5% of the beta-chain which was resistant to proteolytic action. Brief treatment of Kp1 with a lower concentration of chymotrypsin (chymotrypsin/Kp1 ratio = 1:10 by mass, for 10 min) preferentially cleaved high-molecular-mass polypeptides that routinely contaminate preparations of Kp1 prepared by standard procedures. Treatment with chymotrypsin followed by gel filtration to remove the proteinase and cleaved protein fragments can therefore be used to increase significantly the specific activity of Kp1 preparations and remove contaminating activities, such as the ATPase activity of myokinase.

scholarly journals Isolation and characterization of nitrogenase MoFe protein from the mutant strain pHK17 of Klebsiella pneumoniae in which the two bridging cysteine residues of the P-clusters are replaced by the non-coordinating amino acid alanine

1996 ◽  
Vol 318 (1) ◽  
pp. 111-118 ◽  
Author(s):  
Faridoon K YOUSAFZAI ◽  
Martin BUCK ◽  
Barry E. SMITH
Keyword(s):  
Klebsiella Pneumoniae ◽  
Mutant Strain ◽  
Specific Activity ◽  
Relative Distribution ◽  
Wild Type ◽  
Surface Charges ◽  
Ph Profile ◽  
Mofe Protein ◽  
Isolation And Characterization ◽  
Specific Activities

Nitrogenase MoFe protein (Kp1) from the mutant strain pHK17 of Klebsiella pneumoniae has been purified to give three catalytically active fractions. In this mutant, each of the two bridging cysteine ligands to the P-clusters, α-Cys-89 and β-Cys-94, has been replaced by a non-coordinating residue, alanine. SDS/PAGE and earlier native gels showed that the three fractions retained the normal α2β2 tetrameric form of wild-type Kp1; therefore we conclude that in each of the fractions the subunits are folded differently, thus resulting in different surface charges and allowing separation of the fractions on ion-exchange chromatography. Earlier EPR and magnetic CD data had shown that the mutant fractions contain P-clusters, and thus the mutated residues are not as essential for maintaining the integrity of the P-clusters as they appear from the X-ray structure. The specific activity of each of the three fractions was less than that of wild-type Kp1, the most active fraction having only 50% of wild-type activity. No change in substrate specificity or in the relative distribution of electrons to various substrates was found. The relationship between ATP hydrolysis and substrate-reducing activity, the EPR spectra of the S = 3/2 spin state of the iron–molybdenum cofactor (FeMoco) and the pH profile of acetylene-reduction activities of the three fractions did not differ significantly from those exhibited by wild-type Kp1. The specific activities of the three mutant fractions and of wild-type Kp1 were linearly proportional to the intensity of the S = 3/2 EPR signal from the FeMoco centres. This implies that those molecules of the three mutant fractions and the wild-type protein that contain EPR-active FeMoco are fully active, i.e. that the Cys to Ala substitution of the P-cluster ligands does not affect the specific activity of the protein. This in turn implies that the P-clusters are not directly associated with the rate-limiting step in enzyme turnover. We conclude that the lower specific activities of the mutant fractions are observed because the fractions are mixtures of species containing a full complement of FeMoco and P-clusters and species lacking some or all of these clusters. On the basis of the Mo contents and EPR spectroscopy of the mutant fractions, we propose that the loss of the P-clusters causes (i) the physical loss or inhibition of binding of some FeMoco; (ii) the EPR and catalytic inactivation of some FeMoco; and/or (iii) the incorporation of a FeMoco-like species into the FeMoco site of the mutant molecules.

scholarly journals Purification and Characterization of Wild-type and Mutant “Classical” Nitroreductases ofSalmonella typhimurium

1998 ◽  
Vol 273 (37) ◽  
pp. 23922-23928 ◽  
Author(s):  
Masahiko Watanabe ◽  
Tatsuya Nishino ◽  
Koji Takio ◽  
Toshio Sofuni ◽  
Takehiko Nohmi
Keyword(s):  
Wild Type ◽  
Purification And Characterization

Molecular characterization of three mutations in katG affecting the activity of hydroperoxidase I of Escherichia coli

1990 ◽  
Vol 68 (7-8) ◽  
pp. 1037-1044 ◽  
Author(s):  
Peter C. Loewen ◽  
Jacek Switala ◽  
Mark Smolenski ◽  
Barbara L. Triggs-Raine
Keyword(s):  
Escherichia Coli ◽  
Specific Activity ◽  
Polymerase Chain Reaction Amplification ◽  
Protein A ◽  
Wild Type ◽  
Wild Type Enzyme ◽  
Gene Encoding ◽  
Reaction Amplification ◽  
Mutant Genes

Hydroperoxidase I (HPI) of Escherichia coli is a bifunctional enzyme exhibiting both catalase and peroxidase activities. Mutants lacking appreciable HPI have been generated using nitrosoguanidine and the gene encoding HPI, katG, has been cloned from three of these mutants using either classical probing methods or polymerase chain reaction amplification. The mutant genes were sequenced and the changes from wild-type sequence identified. Two mutants contained G to A changes in the coding strand, resulting in glycine to aspartate changes at residues 119 (katG15) and 314 (katG16) in the deduced amino acid sequence of the protein. A third mutant contained a C to T change resulting in a leucine to phenylalanine change at residue 139 (katG14). The Phe139-, Asp119-, and Asp314-containing mutants exhibited 13, < 1, and 18%, respectively, of the wild-type catalase specific activity and 43, 4, and 45% of the wild-type peroxidase specific activity. All mutant enzymes bound less protoheme IX than the wild-type enzyme. The sensitivities of the mutant enzymes to the inhibitors hydroxylamine, azide, and cyanide and the activators imidazole and Tris were similar to those of the wild-type enzyme. The mutant enzymes were more sensitive to high temperature and to β-mercaptoethanol than the wild-type enzyme. The pH profiles of the mutant catalases were unchanged from the wild-type enzyme.Key words: catalase, hydroperoxidase I, mutants, sequence analysis.

Purification and characterization of two isoforms of native α amylase from Ok-Rong mango (Mangifera indica Linn. cv. Ok-Rong)

2017 ◽  
Vol 42 (6) ◽  
Author(s):  
Raksmont Ubonbal ◽  
Saijai Porsoongnoen ◽  
Jureerut Daduang ◽  
Sompong Klaynongsruang ◽  
Sakda Daduang
Keyword(s):  
High Temperatures ◽  
Fruit Ripening ◽  
Specific Activity ◽  
Mangifera Indica ◽  
Ripening Stage ◽  
Purification And Characterization ◽  
Tropical Plant ◽  
Short Period ◽  
Structure Properties

AbstractIntroduction:The tropical plant amylases involved in the fruit ripening stage is outstanding for their high activities in converting starch to sugars within a short period at high temperatures over 40°C.Methods:The α amylase iso-enzymes from Ok-Rong mango (Results:The enzyme was purified 105-fold with a final specific activity of 59.27 U mgConclusion:Two α amylase iso-enzymes were classified as members of the low-pI group of amylases with identical structure, properties and functions. They are mesophilic with high possibilities for application for many purposes.

scholarly journals Purification and Characterization of Endoglucanase from local isolate of Aspergillus flavus

2013 ◽  
Vol 10 (3) ◽  
pp. 844-853
Author(s):  
Baghdad Science Journal
Keyword(s):  
Aspergillus Flavus ◽  
Specific Activity ◽  
Gel Filtration ◽  
Temperature Stability ◽  
Exchange Chromatography ◽  
Purification And Characterization ◽  
Original Activity ◽  
A Value ◽  
Optimum Ph

Endoglucanase produced from Aspergillus flavus was purified by several steps including precipitation with 25 % ammonium sulphate followed by Ion –exchange chromatography, the obtained specific activity was 377.35 U/ mg protein, with a yield of 51.32 % .This step was followed by gel filtration chromatography (Sepharose -6B), when a value of specific activity was 400 U/ mg protein, with a yield of 48 %. Certain properties of this purified enzyme were investigated, the optimum pH of activity was 7 and the pH of its stability was 4.5, while the temperature stability was 40 °C for 60 min. The enzyme retained 100% of its original activity after incubation at 40 °C for 60 min; the optimum temperature for enzyme activity was 40 °C.

The metallo-sulphur centres of the nitrogenase MoFe protein (Kp1) from wild-type and mutant strains of Klebsiella pneumoniae.

1993 ◽  
Vol 51 (1-2) ◽  
pp. 348
Author(s):  
B.E. Smith ◽  
M. Buck ◽  
K.Y. Faridoon ◽  
C.A. Gormal ◽  
B.D. Howes ◽  
...  
Keyword(s):  
Klebsiella Pneumoniae ◽  
Wild Type ◽  
Mofe Protein ◽  
Mutant Strains
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