scholarly journals Spectroscopic Characterisation of the Naphthalene Dioxygenase from Rhodococcus sp. Strain NCIMB12038

2019 ◽  
Vol 20 (14) ◽  
pp. 3402 ◽  
Author(s):  
Maria Camilla Baratto ◽  
David A. Lipscomb ◽  
Michael J. Larkin ◽  
Riccardo Basosi ◽  
Christopher C. R. Allen ◽  
...  
Keyword(s):  
Aromatic Compounds ◽  
Halogenated Hydrocarbons ◽  
Alternative Mechanism ◽  
Naphthalene Dioxygenase ◽  
Epr Spectrum ◽  
Paramagnetic Resonance ◽  
Potential Health ◽  
Polycyclic Aromatic ◽  
Mutagenic Effects ◽  
Rhodococcus Sp

Polycyclic aromatic hydrocarbons (PAHs), such as naphthalene, are potential health risks due to their carcinogenic and mutagenic effects. Bacteria from the genus Rhodococcus are able to metabolise a wide variety of pollutants such as alkanes, aromatic compounds and halogenated hydrocarbons. A naphthalene dioxygenase from Rhodococcus sp. strain NCIMB12038 has been characterised for the first time, using electron paramagnetic resonance (EPR) spectroscopy and UV-Vis spectrophotometry. In the native state, the EPR spectrum of naphthalene 1,2-dioxygenase (NDO) is formed of the mononuclear high spin Fe(III) state contribution and the oxidised Rieske cluster is not visible as EPR-silent. In the presence of the reducing agent dithionite a signal derived from the reduction of the [2Fe-2S] unit is visible. The oxidation of the reduced NDO in the presence of O2-saturated naphthalene increased the intensity of the mononuclear contribution. A study of the “peroxide shunt”, an alternative mechanism for the oxidation of substrate in the presence of H2O2, showed catalysis via the oxidation of mononuclear centre while the Rieske-type cluster is not involved in the process. Therefore, the ability of these enzymes to degrade recalcitrant aromatic compounds makes them suitable for bioremediative applications and synthetic purposes.

scholarly journals Structure and Increased Thermostability of Rhodococcus sp. Naphthalene 1,2-Dioxygenase

2005 ◽  
Vol 187 (21) ◽  
pp. 7222-7231 ◽  
Author(s):  
Lokesh Gakhar ◽  
Zulfiqar A. Malik ◽  
Christopher C. R. Allen ◽  
David A. Lipscomb ◽  
Michael J. Larkin ◽  
...  
Keyword(s):  
Active Site ◽  
Aromatic Compounds ◽  
Guanidine Hydrochloride ◽  
Salt Bridge ◽  
Nonheme Iron ◽  
Mean Square ◽  
Naphthalene Dioxygenase ◽  
Sequence Identity ◽  
Bridge Networks ◽  
Rhodococcus Sp

ABSTRACT Rieske nonheme iron oxygenases form a large class of aromatic ring-hydroxylating dioxygenases found in microorganisms. These enzymes enable microorganisms to tolerate and even exclusively utilize aromatic compounds for growth, making them good candidates for use in synthesis of chiral intermediates and bioremediation. Studies of the chemical stability and thermostability of these enzymes thus become important. We report here the structure of free and substrate (indole)-bound forms of naphthalene dioxygenase from Rhodococcus sp. strain NCIMB12038. The structure of the Rhodococcus enzyme reveals that, despite a ∼30% sequence identity between these naphthalene dioxygenases, their overall structures superpose very well with a root mean square deviation of less than 1.6 Å. The differences in the active site of the two enzymes are pronounced near the entrance; however, indole binds to the Rhodococcus enzyme in the same orientation as in the Pseudomonas enzyme. Circular dichroism spectroscopy experiments show that the Rhodococcus enzyme has higher thermostability than the naphthalene dioxygenase from Pseudomonas species. The Pseudomonas enzyme has an apparent melting temperature of 55°C while the Rhodococcus enzyme does not completely unfold even at 95°C. Both enzymes, however, show similar unfolding behavior in urea, and the Rhodococcus enzyme is only slightly more tolerant to unfolding by guanidine hydrochloride. Structure analysis suggests that the higher thermostability of the Rhodococcus enzyme may be attributed to a larger buried surface area and extra salt bridge networks between the α and β subunits in the Rhodococcus enzyme.

Radiation Effects on Hollandite Ceramics developed for Radioactive Cesium Immobilization

2003 ◽  
Vol 792 ◽  
Author(s):  
V. Aubin ◽  
D. Caurant ◽  
D. Gourier ◽  
N. Baffier ◽  
S. Esnouf ◽  
...  
Keyword(s):  
Radiation Effects ◽  
Liquid Waste ◽  
Fission Products ◽  
Radioactive Cesium ◽  
Radioactive Liquid Waste ◽  
Epr Spectrum ◽  
Paramagnetic Resonance ◽  
Γ Radiation ◽  
The Stability ◽  
High Level

ABSTRACTProgress on separating the long-lived fission products from the high level radioactive liquid waste (HLW) has led to the development of specific host matrices, notably for the immobilization of cesium. Hollandite (nominally BaAl2Ti6O16), one of the main phases constituting Synroc, receives renewed interest as specific Cs-host wasteform. The radioactive cesium isotopes consist of short-lived Cs and Cs of high activities and Cs with long lifetime, all decaying according to Cs+→Ba2++e- (β) + γ. Therefore, Cs-host forms must be both heat and (β,γ)-radiation resistant. The purpose of this study is to estimate the stability of single phase hollandite under external β and γ radiation, simulating the decay of Cs. A hollandite ceramic of simple composition (Ba1.16Al2.32Ti5.68O16) was essentially irradiated by 1 and 2.5 MeV electrons with different fluences to simulate the β particles emitted by cesium. The generation of point defects was then followed by Electron Paramagnetic Resonance (EPR). All these electron irradiations generated defects of the same nature (oxygen centers and Ti3+ ions) but in different proportions varying with electron energy and fluence. The annealing of irradiated samples lead to the disappearance of the latter defects but gave rise to two other types of defects (aggregates of light elements and titanyl ions). It is necessary to heat at relatively high temperature (T=800°C) to recover an EPR spectrum similar to that of the pristine material. The stability of hollandite phase under radioactive cesium irradiation during the waste storage is discussed.

Rapid Construction of Fold-Line-Shaped BN-Embedded Polycyclic Aromatic Compounds through Diels–Alder Reaction

2019 ◽  
Vol 85 (1) ◽  
pp. 241-247
Author(s):  
Peng-Fei Zhang ◽  
Fang-Dong Zhuang ◽  
Ze-Hao Sun ◽  
Yang Lu ◽  
Jie-Yu Wang ◽  
...  
Keyword(s):  
Aromatic Compounds ◽  
Alder Reaction ◽  
Diels Alder ◽  
Polycyclic Aromatic Compounds ◽  
Diels Alder Reaction ◽  
Fold Line ◽  
Rapid Construction ◽  
Polycyclic Aromatic
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