Photosensitized Electron Transfer Oxidation of Sulfides: A Steady-State Study

2008 ◽  
Vol 2008 (15) ◽  
pp. 2612-2620 ◽  
Author(s):  
Sergio M. Bonesi ◽  
Maurizio Fagnoni ◽  
Angelo Albini
Keyword(s):  
Electron Transfer ◽  
Steady State ◽  
Oxidation Of Sulfides ◽  
State Study

NON-STEADY STATE STUDY ON THE BASE HYDROLYSIS OF MONOIODOPENTAAMMINERUTHENIUM(III) COMPLEX

1975 ◽  
Vol 4 (7) ◽  
pp. 631-634 ◽  
Author(s):  
Hiroyuki Sakamoto ◽  
Haruo Makino ◽  
Keijiro Hamada ◽  
Akira Ohyoshi
Keyword(s):  
Steady State ◽  
Base Hydrolysis ◽  
State Study ◽  
Hydrolysis Of

scholarly journals The importance of the interdomain hinge in intramolecular electron transfer in flavocytochrome b2

1993 ◽  
Vol 291 (1) ◽  
pp. 89-94 ◽  
Author(s):  
P White ◽  
F D C Manson ◽  
C E Brunt ◽  
S K Chapman ◽  
G A Reid
Keyword(s):  
Electron Transfer ◽  
Steady State ◽  
Cytochrome C ◽  
Kinetic Properties ◽  
Stopped Flow ◽  
Wild Type ◽  
Wild Type Enzyme ◽  
Cytochrome C Reductase ◽  
Flavocytochrome B2 ◽  
Cytochrome C Reduction

The two distinct domains of flavocytochrome b2 (L-lactate:cytochrome c oxidoreductase) are connected by a typical hinge peptide. The amino acid sequence of this interdomain hinge is dramatically different in flavocytochromes b2 from Saccharomyces cerevisiae and Hansenula anomala. This difference in the hinge is believed to contribute to the difference in kinetic properties between the two enzymes. To probe the importance of the hinge, an interspecies hybrid enzyme has been constructed comprising the bulk of the S. cerevisiae enzyme but containing the H. anomala flavocytochrome b2 hinge. The kinetic properties of this ‘hinge-swap’ enzyme have been investigated by steady-state and stopped-flow methods. The hinge-swap enzyme remains a good lactate dehydrogenase as is evident from steady-state experiments with ferricyanide as acceptor (only 3-fold less active than wild-type enzyme) and stopped-flow experiments monitoring flavin reduction (2.5-fold slower than in wild-type enzyme). The major effect of the hinge-swap mutation is to lower dramatically the enzyme's effectiveness as a cytochrome c reductase; kcat. for cytochrome c reduction falls by more than 100-fold, from 207 +/- 10 s-1 (25 degrees C, pH 7.5) in the wild-type enzyme to 1.62 +/- 0.41 s-1 in the mutant enzyme. This fall in cytochrome c reductase activity results from poor interdomain electron transfer between the FMN and haem groups. This can be demonstrated by the fact that the kcat. for haem reduction in the hinge-swap enzyme (measured by the stopped-flow method) has a value of 1.61 +/- 0.42 s-1, identical with the value for cytochrome c reduction and some 300-fold lower than the value for the wild-type enzyme. From these and other kinetic parameters, including kinetic isotope effects with [2-2H]lactate, we conclude that the hinge plays a crucial role in allowing efficient electron transfer between the two domains of flavocytochrome b2.

scholarly journals Studies on the electron-transfer mechanism of the human neutrophil NADPH oxidase

1989 ◽  
Vol 262 (2) ◽  
pp. 575-579 ◽  
Author(s):  
J A Ellis ◽  
A R Cross ◽  
O T G Jones
Keyword(s):  
Electron Transfer ◽  
Steady State ◽  
Nadph Oxidase ◽  
Cytochrome B ◽  
Human Neutrophil ◽  
Sodium Deoxycholate ◽  
Human Neutrophils ◽  
Electron Transfer Mechanism ◽  
State Reduction ◽  
O2 Production

A superoxide-generating NADPH oxidase was solubilized from phorbol 12-myristate 13-acetate-activated human neutrophils with a mixture of sodium deoxycholate (0.125%, w/v) and Lubrol-PX (0.125%, v/v). The solubilized preparation contained FAD (577 pmol/mg of protein) and cytochrome b-245 (479 pmol/mg of protein) and produced 11.61 mol of O2-./s per mol of cytochrome b (340 nmol of O2-./min per mg of protein). On addition of NADPH, the cytochrome b-245 was reduced by 7.9% and the FAD by 38% in the aerobic steady state; NADH addition caused little steady-state reduction of cytochrome b and FAD. In this preparation, and several others, the measured rate of O2-. production correlated with the turnover of cytochrome b calculated from the extent of cytochrome b-245 reduction under aerobic conditions. Addition of diphenyleneiodonium abolished the reduction of both the FAD and cytochrome b-245 components and inhibited O2-. production. The haem ligand imidazole inhibited O2-. generation and cytochrome b reduction while permitting FAD reduction. These results support the suggestion that the human neutrophil NADPH oxidase has the electron-transport sequence: NADPH-FAD-cytochrome b-245-O2.

scholarly journals Copper(II) Thiosemicarbazone Complexes and Their Proligands upon UVA Irradiation: An EPR and Spectrophotometric Steady-State Study

Molecules ◽  
2018 ◽  
Vol 23 (4) ◽  
pp. 721 ◽  
Author(s):  
Michal Hricovíni ◽  
Milan Mazúr ◽  
Angela Sîrbu ◽  
Oleg Palamarciuc ◽  
Vladimir Arion ◽  
...  
Keyword(s):  
Steady State ◽  
Uva Irradiation ◽  
State Study ◽  
Thiosemicarbazone Complexes

Fast-Tracking an FLNG Relocation in Malaysia

2021 ◽  
Vol 73 (04) ◽  
pp. 39-40
Author(s):  
Judy Feder
Keyword(s):  
Steady State ◽  
Cost Minimization ◽  
Flow Assurance ◽  
Transient Operation ◽  
Fast Tracking ◽  
Engineering Studies ◽  
Offshore Technology ◽  
State Study ◽  
Common Support ◽  
Minimal Modification

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper OTC 30440, “Floating LNG 1 Relocation: Another World’s First,” by Muhammad Fakhruddin Jais, Wan Mahsuri Wan Hashim, and Ariff Azhari Ayadali, Petronas, et al., prepared for the 2020 Offshore Technology Conference Asia, originally scheduled to be held in Kuala Lumpur, Malaysia, 17–19 August. The paper has not been peer reviewed. Copyright 2020 Offshore Technology Conference. Reproduced by permission. Floating liquefied natural gas (FLNG) allows LNG to be processed hundreds of kilometers away from land to unlock gas reserves in remote and stranded fields previously uneconomical to monetize. The complete paper describes the operator’s fast-tracking of a 450-km FLNG unit relocation from Sarawak to Sabah offshore Malaysia. The time from selecting the new field to unloading LNG at the new location was 13 months. The complete paper discusses pre-execution and engineering studies, relocation preparation and execution, and challenges encountered, including timeline, cost minimization, and manning. Introduction Since 2016, Petronas has operated its first floating LNG production, storage, and offloading facility offshore Sarawak. During the tenure of operation, cargo was delivered successfully to customers worldwide. An opportunity to help a different gas supplier monetize another stranded field offshore Sabah, approximately 450 km away from the unit’s original location, presented itself. The new opportunity was deemed feasible for several reasons. - The identified location is still within Malaysian waters and thus is subject to similar authority and regulations. - Operation within the same country ensures common support from vendor and contractors to some extent. - The two fields have similar gas profiles and water depth. The project team determined that these factors would result in minimal modification at both FLNG and up-stream facilities to meet minimum shut-down from project sanction until first LNG cargo was produced. Pre-Execution and Engineering Studies To fast-track the project, an evaluation was conducted of the new feed-gas composition and modification of both up-stream and FLNG facilities. Long-lead items (LLIs) were identified, and studies were conducted to secure the items. One of the identified LLIs was the flexible pipeline from the upstream facilities to the FLNG. A flow-assurance study covered the steady-state and transient operation for the flexible line. This study confirmed the size of the pipeline and defined the functional requirement for the flexible pipeline procurement. Among the key parameters identified were the pipeline’s thermal conductivity and design pressure. During the feasibility stage, a steady-state study was conducted to determine the length of the flexible line in order to meet the landing pressure and temperature at the FLNG. Instead of requiring additional cooler, the flexible line was extended 2 km to take advantage of the Joule-Thomson cooling effect resulting from the pressure drop across the pipeline. In addition to defining the LLI properties, the flow-assurance study also examined the transient operation for both upstream and FLNG upon the closure of the riser shutdown valve. The study assessed flow-assurance issues, such as hydrates and adequacy of the slug receiver during the transient operation, that might arise, and defined the start-up and commissioning sequence for the facilities.

The oxidation of sulfides by chromium(V)

2003 ◽  
Vol 81 (1) ◽  
pp. 75-80 ◽  
Author(s):  
Carmela R Jackson Lepage ◽  
Lynn Mihichuk ◽  
Donald G Lee
Keyword(s):  
Electron Transfer ◽  
Molecular Orbital ◽  
Radical Cation ◽  
Oxygen Transfer ◽  
Single Electron ◽  
Frontier Molecular Orbital ◽  
Molecular Orbital Calculations ◽  
Single Electron Transfer ◽  
Oxidation Of Sulfides

The mechanism for the oxidation of sulfides by [(me4-salen)CrV(O)(pyO)]CF3SO3, where me4-salen is 8,8,8',8'-tetramethylsalen and pyO is pyridine N-oxide, has been investigated. Results from Hammett correlations on the rates of oxidation of substituted thioanisoles, frontier molecular orbital calculations, and product studies are consistent with a mechanism that is initiated by a single electron transfer to give a radical cation intermediate.Key words: oxidation, chromium(V), sulfides, radical cation, oxygen transfer.

scholarly journals Tyr-143 facilitates interdomain electron transfer in flavocytochrome b2

1992 ◽  
Vol 285 (1) ◽  
pp. 187-192 ◽  
Author(s):  
C S Miles ◽  
N Rouvière-Fourmy ◽  
F Lederer ◽  
F S Mathews ◽  
G A Reid ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Steady State ◽  
Isotope Effects ◽  
Mutant Enzyme ◽  
Stopped Flow ◽  
Wild Type ◽  
Wild Type Enzyme ◽  
Flavocytochrome B2 ◽  
Rate Determining Step ◽  
Kinetic Isotope

The role of Tyr-143 in the catalytic cycle of flavocytochrome b2 (L-lactate:cytochrome c oxidoreductase) has been examined by replacement of this residue with phenylalanine. The electron-transfer steps in wild-type and mutant flavocytochromes b2 have been investigated by using steady-state and stopped-flow kinetic methods. The most significant effect of the Tyr-143----Phe mutation is a change in the rate-determining step in the reduction of the enzyme. For wild-type enzyme the main rate-determining step is proton abstraction at the C-2 position of lactate, as shown by the 2H kinetic-isotope effect. However, for the mutant enzyme it is clear that the slowest step is interdomain electron transfer between the FMN and haem prosthetic groups. In fact, the rate of haem reduction by lactate, as determined by the stopped-flow method, is decreased by more than 20-fold, from 445 +/- 50 s-1 (25 degrees C, pH 7.5) in the wild-type enzyme to 21 +/- 2 s-1 in the mutant enzyme. Decreases in kinetic-isotope effects seen with [2-2H]lactate for mutant enzyme compared with wild-type, both for flavin reduction (from 8.1 +/- 1.4 to 4.3 +/- 0.8) and for haem reduction (from 6.3 +/- 1.2 to 1.6 +/- 0.5) also provide support for a change in the nature of the rate-determining step. Other kinetic parameters determined by stopped-flow methods and with two external electron acceptors (cytochrome c and ferricyanide) under steady-state conditions are all consistent with this mutation having a dramatic effect on interdomain electron transfer. We conclude that Tyr-143, an active-site residue which lies between the flavodehydrogenase and cytochrome domains of flavocytochrome b2, plays a key role in facilitating electron transfer between FMN and haem groups.

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