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

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 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 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 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+.

scholarly journals Steady-state kinetics and inhibition of anaerobically purified human homogentisate 1,2-dioxygenase

2005 ◽  
Vol 386 (2) ◽  
pp. 305-314 ◽  
Author(s):  
Edwin J. A. VELDHUIZEN ◽  
Frédéric H. VAILLANCOURT ◽  
Cheryl J. WHITING ◽  
Marvin M.-Y. HSIAO ◽  
Geneviève GINGRAS ◽  
...  
Keyword(s):  
Steady State ◽  
Active Site ◽  
Ternary Complex ◽  
Specific Activity ◽  
Complex Mechanism ◽  
Substrate Analogues ◽  
Steady State Kinetics ◽  
Km Value ◽  
Substrate Concentrations ◽  
Active Preparation

HGO (homogentisate 1,2-dioxygenase; EC 1.13.11.5) catalyses the O2-dependent cleavage of HGA (homogentisate) to maleylacetoacetate in the catabolism of tyrosine. Anaerobic purification of heterologously expressed Fe(II)-containing human HGO yielded an enzyme preparation with a specific activity of 28.3± 0.6 μmol·min−1·mg−1 (20 mM Mes, 80 mM NaCl, pH 6.2, 25 °C), which is almost twice that of the most active preparation described to date. Moreover, the addition of reducing agents or other additives did not increase the specific activity, in contrast with previous reports. The apparent specificity of HGO for HGA was highest at pH 6.2 and the steady-state cleavage of HGA fit a compulsory-order ternary-complex mechanism (Km value of 28.6±6.2 μM for HGA, Km value of 1240±160 μM for O2). Free HGO was subject to inactivation in the presence of O2 and during the steady-state cleavage of HGA. Both cases involved the oxidation of the active site Fe(II). 3-Cl HGA, a potential inhibitor of HGO, and its isosteric analogue, 3-Me HGO, were synthesized. At saturating substrate concentrations, HGO cleaved 3-Me and 3-Cl HGA 10 and 100 times slower than HGA respectively. The apparent specificity of HGO for HGA was approx. two orders of magnitude higher than for either 3-Me or 3-Cl HGA. Interestingly, 3-Cl HGA inactivated HGO only twice as rapidly as HGA. This contrasts with what has been observed in mechanistically related dioxygenases, which are rapidly inactivated by chlorinated substrate analogues, such as 3-hydroxyanthranilate dioxygenase by 4-Cl 3-hydroxyanthranilate.

scholarly journals The Kinetics of Product Inhibition in the Ternary-Complex Mechanism for Enzyme Reactions Involving Two Substrates.

1972 ◽  
Vol 26 ◽  
pp. 3935-3942 ◽  
Author(s):  
Gösta Pettersson ◽  
Kjell Undheim ◽  
P. Klæboe ◽  
T. Torgrimsen ◽  
Åke Pilotti
Keyword(s):  
Ternary Complex ◽  
Product Inhibition ◽  
Complex Mechanism ◽  
Enzyme Reactions ◽  
Kinetics Of
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