Kinetic Model for the Regulation by Substrate of Intramolecular Electron Transfer in Trimethylamine Dehydrogenase†

Biochemistry ◽  
1996 ◽  
Vol 35 (7) ◽  
pp. 2445-2452 ◽  
Author(s):  
Liliana Falzon ◽  
Victor L. Davidson
Keyword(s):  
Electron Transfer ◽  
Kinetic Model ◽  
Intramolecular Electron Transfer ◽  
Trimethylamine Dehydrogenase

scholarly journals Mechanistic studies on the dehydrogenases of methylotrophic bacteria. 2. Kinetic studies on the intramolecular electron transfer in trimethylamine and dimethylamine dehydrogenase

1982 ◽  
Vol 207 (2) ◽  
pp. 241-252 ◽  
Author(s):  
D J Steenkamp ◽  
H Beinert
Keyword(s):  
Electron Transfer ◽  
Triplet State ◽  
Substrate Inhibition ◽  
Kinetic Studies ◽  
Reduced Form ◽  
Intramolecular Electron Transfer ◽  
Methylotrophic Bacteria ◽  
Trimethylamine Dehydrogenase ◽  
Substrate Dependence ◽  
Reduced Forms

E.p.r. spectroscopy of the trimethylamine and dimethylamine dehydrogenases of Hyphomicrobium X indicates that the substrate-reduced forms of these enzymes exist in the triplet state, which arise through interaction of a reduced [4Fe-4S] cluster and flavosemiquinone, with e.p.r. signals which differ in detail from those of the trimethylamine dehydrogenase of bacterium W3A1. Under certain conditions the intramolecular electron transfer between the flavoquinol form of 6-S-cysteinyl-FMN and the [4Fe-4S] cluster in all three dehydrogenases was much slower than the preceding reduction of the flavin to the flavoquinol form. Trimethylamine dehydrogenases from both organisms show a time-dependent broadening of the e.p.r. signals centred around g = 2 after mixing with trimethylamine. The broadening of the e.p.r. signals could be correlated with an unexpected dependence of the rate of formation of the triplet state on substrate concentration. A model which accounts in a qualitative manner for the substrate dependence of the formation of the triplet state in the trimethylamine dehydrogenase of Hyphomicrobium X is proposed. The binding of the substrate to the reduced form of the enzyme seems to result in a conformational change of the enzyme to a form in which the rate of intramolecular electron transfer is decreased. This finding may be correlated with the observation of hyperbolic substrate inhibition for both trimethylamine dehydrogenases. The results indicate the transfer of an electron to the [4Fe-4S] cluster to be an obligatory step in catalysis and suggest that the transfer of electrons from these enzymes to electron acceptors is mediated solely through the [4Fe-4S] cluster.

Flavin radicals, conformational sampling and robust design principles in interprotein electron transfer: the trimethylamine dehydrogenase-electron-transferring flavoprotein complex

2004 ◽  
Vol 71 ◽  
pp. 1-14
Author(s):  
David Leys ◽  
Jaswir Basran ◽  
François Talfournier ◽  
Kamaldeep K. Chohan ◽  
Andrew W. Munro ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Dimensional Space ◽  
Three Dimensional ◽  
Kinetic Studies ◽  
Molecular Assembly ◽  
Conformational Sampling ◽  
Trimethylamine Dehydrogenase ◽  
Key Residues ◽  
Electron Transferring Flavoprotein ◽  
Electron Transfer Complex

TMADH (trimethylamine dehydrogenase) is a complex iron-sulphur flavoprotein that forms a soluble electron-transfer complex with ETF (electron-transferring flavoprotein). The mechanism of electron transfer between TMADH and ETF has been studied using stopped-flow kinetic and mutagenesis methods, and more recently by X-ray crystallography. Potentiometric methods have also been used to identify key residues involved in the stabilization of the flavin radical semiquinone species in ETF. These studies have demonstrated a key role for 'conformational sampling' in the electron-transfer complex, facilitated by two-site contact of ETF with TMADH. Exploration of three-dimensional space in the complex allows the FAD of ETF to find conformations compatible with enhanced electronic coupling with the 4Fe-4S centre of TMADH. This mechanism of electron transfer provides for a more robust and accessible design principle for interprotein electron transfer compared with simpler models that invoke the collision of redox partners followed by electron transfer. The structure of the TMADH-ETF complex confirms the role of key residues in electron transfer and molecular assembly, originally suggested from detailed kinetic studies in wild-type and mutant complexes, and from molecular modelling.

Intramolecular Electron Transfer Mediated by a Tetrathiafulvalene Bridge in a Purely Organic Mixed-Valence System

2003 ◽  
Vol 42 (24) ◽  
pp. 2765-2768 ◽  
Author(s):  
Nicolas Gautier ◽  
Frédéric Dumur ◽  
Vega Lloveras ◽  
José Vidal-Gancedo ◽  
Jaume Veciana ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Mixed Valence ◽  
Intramolecular Electron Transfer
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