scholarly journals A Glutathione S-Transferase Catalyzes the Dehalogenation of Inhibitory Metabolites of Polychlorinated Biphenyls

2006 ◽  
Vol 188 (12) ◽  
pp. 4424-4430 ◽  
Author(s):  
Pascal D. Fortin ◽  
Geoff P. Horsman ◽  
Hao M. Yang ◽  
Lindsay D. Eltis
Keyword(s):  
Reaction Mechanism ◽  
Polychlorinated Biphenyls ◽  
Ternary Complex ◽  
Physiological Function ◽  
Complex Mechanism ◽  
Glutathione S Transferase ◽  
Burkholderia Xenovorans ◽  
Pcb Metabolites

ABSTRACT BphK is a glutathione S-transferase of unclear physiological function that occurs in some bacterial biphenyl catabolic (bph) pathways. We demonstrated that BphK of Burkholderia xenovorans strain LB400 catalyzes the dehalogenation of 3-chloro 2-hydroxy-6-oxo-6-phenyl-2,4-dienoates (HOPDAs), compounds that are produced by the cometabolism of polychlorinated biphenyls (PCBs) by the bph pathway and that inhibit the pathway's hydrolase. A one-column protocol was developed to purify heterologously produced BphK. The purified enzyme had the greatest specificity for 3-Cl HOPDA (k cat/Km , ∼104 M−1 s−1), which it dechlorinated approximately 3 orders of magnitude more efficiently than 4-chlorobenzoate, a previously proposed substrate of BphK. The enzyme also catalyzed the dechlorination of 5-Cl HOPDA and 3,9,11-triCl HOPDA. By contrast, BphK did not detectably transform HOPDA, 4-Cl HOPDA, or chlorinated 2,3-dihydroxybiphenyls. The BphK-catalyzed dehalogenation proceeded via a ternary-complex mechanism and consumed 2 equivalents of glutathione (GSH) (Km for GSH in the presence of 3-Cl HOPDA, ∼0.1 mM). A reaction mechanism consistent with the enzyme's specificity is proposed. The ability of BphK to dehalogenate inhibitory PCB metabolites supports the hypothesis that this enzyme was recruited to facilitate PCB degradation by the bph pathway.

scholarly journals Degradation Products of Polychlorinated Biphenyls and Their In Vitro Transformation by Ligninolytic Fungi

Toxics ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 81
Author(s):  
Kamila Šrédlová ◽  
Kateřina Šírová ◽  
Tatiana Stella ◽  
Tomáš Cajthaml
Keyword(s):  
Polychlorinated Biphenyls ◽  
Extracellular Enzymes ◽  
Degradation Products ◽  
Transformation Products ◽  
Irpex Lacteus ◽  
Chlorobenzoic Acid ◽  
Ligninolytic Fungi ◽  
Wide Range ◽  
Pcb Metabolites

Metabolites of polychlorinated biphenyls (PCBs)—hydroxylated PCBs (OH‑PCBs), chlorobenzyl alcohols (CB‑OHs), and chlorobenzaldehydes (CB‑CHOs)—were incubated in vitro with the extracellular liquid of Pleurotus ostreatus, which contains mainly laccase and low manganese-dependent peroxidase (MnP) activity. The enzymes were able to decrease the amount of most of the tested OH‑PCBs by > 80% within 1 h; the removal of more recalcitrant OH‑PCBs was greatly enhanced by the addition of the laccase mediator syringaldehyde. Conversely, glutathione substantially hindered the reaction, suggesting that it acted as a laccase inhibitor. Hydroxylated dibenzofuran and chlorobenzoic acid were identified as transformation products of OH‑PCBs. The extracellular enzymes also oxidized the CB‑OHs to the corresponding CB‑CHOs on the order of hours to days; however, the mediated and nonmediated setups exhibited only slight differences, and the participating enzymes could not be determined. When CB‑CHOs were used as the substrates, only partial transformation was observed. In an additional experiment, the extracellular liquid of Irpex lacteus, which contains predominantly MnP, was able to efficiently transform CB‑CHOs with the aid of glutathione; mono‑ and di-chloroacetophenones were detected as transformation products. These results demonstrate that extracellular enzymes of ligninolytic fungi can act on a wide range of PCB metabolites, emphasizing their potential for bioremediation.

scholarly journals Enzyme-Like Catalysis via Ternary Complex Mechanism: Alkoxy-Bridged Dinuclear Cobalt Complex Mediates Chemoselective O-Esterification over N-Amidation

2013 ◽  
Vol 135 (16) ◽  
pp. 6192-6199 ◽  
Author(s):  
Yukiko Hayashi ◽  
Stefano Santoro ◽  
Yuki Azuma ◽  
Fahmi Himo ◽  
Takashi Ohshima ◽  
...  
Keyword(s):  
Ternary Complex ◽  
Cobalt Complex ◽  
Complex Mechanism

Changes in serum concentrations of polychlorinated biphenyls (PCBs), hydroxylated PCB metabolites and pentachlorophenol during pregnancy

Chemosphere ◽  
2011 ◽  
Vol 83 (2) ◽  
pp. 144-151 ◽  
Author(s):  
Anders Glynn ◽  
Maria Larsdotter ◽  
Marie Aune ◽  
Per Ola Darnerud ◽  
Rickard Bjerselius ◽  
...  
Keyword(s):  
Polychlorinated Biphenyls ◽  
Serum Concentrations ◽  
Pcb Metabolites

Agonist high and low affinity state ratios predict drug intrinsic activity and a revised Ternary complex mechanism at serotonin 5-HT2A and 5-HT2C receptors

Synapse ◽  
2000 ◽  
Vol 35 (2) ◽  
pp. 144-150 ◽  
Author(s):  
Christina Egan ◽  
Ellinor Grinde ◽  
Ann Dupre ◽  
Bryan L. Roth ◽  
Michael Hake ◽  
...  
Keyword(s):  
Ternary Complex ◽  
Intrinsic Activity ◽  
Complex Mechanism

scholarly journals Mechanistic origin of the sigmoidal rate behaviour of glucokinase

1986 ◽  
Vol 233 (2) ◽  
pp. 347-350 ◽  
Author(s):  
G Pettersson
Keyword(s):  
Ternary Complex ◽  
Flow Characteristics ◽  
Free Enzyme ◽  
Kinetic Properties ◽  
Complex Mechanism ◽  
Insufficient Evidence ◽  
Conformational States ◽  
Model Studies ◽  
Glucose Binding ◽  
Rate Behaviour

Model studies are presented which demonstrate that reactions proceeding by a random ternary-complex mechanism may exhibit most pronounced deviations from Michaelis-Menten kinetics even if the reaction is effectively ordered with respect to net reaction flow. In particular, the kinetic properties and reaction flow characteristics of glucokinase can be accounted for in such terms. It is concluded that insufficient evidence has been presented to support the idea that glucokinase operates by a ‘mnemonical’ type of mechanism involving glucose binding to distinct conformational states of free enzyme. The sigmoidal rate behaviour of glucokinase can presently be more simply explained in terms of glucose binding to differently ligated states of the enzyme.

scholarly journals Reactivity of Toluate Dioxygenase with Substituted Benzoates and Dioxygen

2002 ◽  
Vol 184 (15) ◽  
pp. 4096-4103 ◽  
Author(s):  
Yong Ge ◽  
Frédéric H. Vaillancourt ◽  
Nathalie Y. R. Agar ◽  
Lindsay D. Eltis
Keyword(s):  
Steady State ◽  
Pseudomonas Putida ◽  
Sodium Phosphate ◽  
Ternary Complex ◽  
Specific Activity ◽  
Complex Mechanism ◽  
Aromatic Substrate ◽  
Steady State Kinetics ◽  
Full Complement

ABSTRACT Toluate dioxygenase (TADO) of Pseudomonas putida mt-2 catalyzes the dihydroxylation of a broad range of substituted benzoates. The two components of this enzyme were hyperexpressed and anaerobically purified. Reconstituted TADO had a specific activity of 3.8 U/mg with m-toluate, and each component had a full complement of their respective Fe2S2 centers. Steady-state kinetics data obtained by using an oxygraph assay and by varying the toluate and dioxygen concentrations were analyzed by a compulsory order ternary complex mechanism. TADO had greatest specificity for m-toluate, displaying apparent parameters of KmA = 9 ± 1 μM, k cat = 3.9 ± 0.2 s−1, and K m O2 = 16 ± 2 μM (100 mM sodium phosphate, pH 7.0; 25°C), where K m O2 represents the K m for O2 and KmA represents the K m for the aromatic substrate. The enzyme utilized benzoates in the following order of specificity: m-toluate > benzoate ≃ 3-chlorobenzoate > p-toluate ≃ 4-chlorobenzoate ≫ o-toluate ≃ 2-chlorobenzoate. The transformation of each of the first five compounds was well coupled to O2 utilization and yielded the corresponding 1,2-cis-dihydrodiol. In contrast, the transformation of ortho-substituted benzoates was poorly coupled to O2 utilization, with >10 times more O2 being consumed than benzoate. However, the apparent K m of TADO for these benzoates was >100 μM, indicating that they do not effectively inhibit the turnover of good substrates.

scholarly journals Acetylcholinesterase and Butyrylcholinesterase – Important Enzymes of Human Body

2004 ◽  
Vol 47 (4) ◽  
pp. 215-228 ◽  
Author(s):  
Jiří Patočka ◽  
Kamil Kuča ◽  
Daniel Jun
Keyword(s):  
Reaction Mechanism ◽  
Peripheral Nerve ◽  
Human Body ◽  
Physiological Function ◽  
Human Tissues ◽  
Serine Hydrolases ◽  
Chemical Reaction Mechanism ◽  
Cholinesterase Activities ◽  
Peripheral Nerve System ◽  
Nerve System

The serine hydrolases and proteases are a ubiquitous group of enzymes that is fundamental to many critical lifefunctions. Human tissues have two distinct cholinesterase activities: acetylcholinesterase and butyrylcholinesterase. Acetylcholinesterase functions in the transmission of nerve impulses, whereas the physiological function of butyrylcholinesterase remains unknown. Acetylcholinesterase is one of the crucial enzymes in the central and peripheral nerve system. Organophosphates and carbamates are potent inhibitors of serine hydrolases and well suited probes for investigating the chemical reaction mechanism of the inhibition. Understanding the enzyme’s chemistry is essential in preventing and/or treating organophosphate and carbamate poisoning as well as designing new medicaments for cholinergic-related diseases like as Alzheimer’s disease.

scholarly journals Bovine lens aldehyde reductase (aldose reductase). Purification, kinetics and mechanism

1984 ◽  
Vol 219 (1) ◽  
pp. 33-39 ◽  
Author(s):  
A B Halder ◽  
M J C Crabbe
Keyword(s):  
Aldose Reductase ◽  
Gel Electrophoresis ◽  
Ternary Complex ◽  
Minimum Degree ◽  
Polyacrylamide Gel Electrophoresis ◽  
Sodium Dodecyl ◽  
Aldehyde Reductase ◽  
Complex Mechanism ◽  
Bovine Lens ◽  
Initial Binding

Aldehyde reductase (aldose reductase) was purified to homogeneity (as judged by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis) from bovine lens by affinity chromatography on NADP+-Sepharose. The enzyme, a monomer of Mr about 40000, was active with a variety of alpha- hydroxyketones, including fructose. The minimum degree of the rate equation was 2:2 in the case of DL-glyceraldehyde, but linear kinetics were observed for glucose and NADPH over the concentration range studied. The enzyme largely followed a ternary-complex mechanism, with initial binding of NADPH before glucose and final release of NADP+.

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