Electron transport system measurement

What should be emphasized is that the redox potentials measured for 10 and 22 allow for both the reduction of 10 to dihydro-10 via F420H2 and H2, and the oxidation of dihydro-10 to 10 by 22. This finding, supported by electrochemical experiments, also strongly corroborates the hypothesis that 10 plays a prominent role as an electron carrier in the electron transport system of methanogens. 

Various methods have been used to estimate water-column denitrification rates including stoichiometric relationships, measurements of the enzymatic activity of the electron transport system (ETS), and N03 incubation experiments. In combination with residence times or mass transport calculations these measurements yield areal denitrification rates. 

Measurement of the enzyme activity of the respiratory electron transport system (ETS activity) has also been used to estimate denitrification rates in the Arabian Sea (Naqvi and Shail a, 1993) and eastern tropical South Pacific (Codispoti and Packard, 1980) denitrification zones. To measure the ETS activity a crude enzyme extract is made by grinding filtered seawater samples in a buffered medium to liberate the enzymes, after which the ETS substrates NADT1+ and NADPT1+ along with tetrazo-hum salt are added as an artificial electron acceptor. Samples are then incubated for a... 

The efficiency of oxidative phosphorylation is determined by the P/O ratio, which is a measure of the molecules of ATP made per pair of electrons carried through the electron transport. Experimentally, researchers isolate mitochondria from cells, then use oxygen electrodes to determine the amount of ATP synthesized per oxygen molecule reduced to water molecules in the last step of the electron transport system. 

The measuring principle of a biosensor designed for pesticide determination is mainly enzyme inhibition. Cyanobacteria, thylakoid membranes, protoplasts, immobilized enzymes, and labeled enzymes are receptor components. The analyte blocks the enzyme, enzyme systems, or electron transport systems of intact cells. 

To measure and analyse the energy-flux-balance EB in biological electron transport systems. The energy-flux-balance is the ratio of the rate of ATP synthesis (dATP/dt) and the rate of electron transport (eg. the production of reducing equivalents dRHa/dt)... 

It should be emphasized here that the four major complexes of the electron transport chain operate quite independently in the inner mitochondrial membrane. Each is a multiprotein aggregate maintained by numerous strong associations between peptides of the complex, but there is no evidence that the complexes associate with one another in the membrane. Measurements of the lateral diffusion rates of the four complexes, of coenzyme Q, and of cytochrome c in the inner mitochondrial membrane show that the rates differ considerably, indicating that these complexes do not move together in the membrane. Kinetic studies with reconstituted systems show that electron transport does not operate by means of connected sets of the four complexes. 

A term that is nearly synonymous with complex numbers or functions is their phase. The rising preoccupation with the wave function phase in the last few decades is beyond doubt, to the extent that the importance of phases has of late become comparable to that of the moduli. (We use Dirac s terminology [7], which writes a wave function by a set of coefficients, the amplitudes, each expressible in terms of its absolute value, its modulus, and its phase. ) There is a related growth of literature on interference effects, associated with Aharonov-Bohm and Berry phases [8-14]. In parallel, one has witnessed in recent years a trend to construct selectively and to manipulate wave functions. The necessary techniques to achieve these are also anchored in the phases of the wave function components. This trend is manifest in such diverse areas as coherent or squeezed states [15,16], electron transport in mesoscopic systems [17], sculpting of Rydberg-atom wavepackets [18,19], repeated and nondemolition quantum measurements [20], wavepacket collapse [21], and quantum computations [22,23]. Experimentally, the determination of phases frequently utilizes measurement of Ramsey fringes [24] or similar methods [25],... 

An interesting experiment is to allow oxidative phosphorylation to proceed until the mitochondria reach state 4 and to measure the phosphorylation state ratio Rp, which equals the value of [ATP] / [ADP][PJ that is attained. This mass action ratio, which has also been called the "phosphorylation ratio" or "phosphorylation potential" (see Chapter 6 and Eq. 6-29), often reaches values greater than 104-105 M 1 in the cytosol.164 An extrapolated value for a zero rate of ATP hydrolysis of log Rf) = 6.9 was estimated. This corresponds (Eq. 6-29) to an increase in group transfer potential (AG of hydrolysis of ATP) of 39 kj/mol. It follows that the overall value of AG for oxidation of NADH in the coupled electron transport chain is less negative than is AG. If synthesis of three molecules of ATP is coupled to electron transport, the system should reach an equilibrium when Rp = 106 4 at 25°C, the difference in AG and AG being 3RT In Rp = 3 x 5.708 x 6.4 = 110 kj mol-1. This value of Rp is, within experimental error, the same as the maximum value observed.165 There apparently is an almost true equilibrium among NADH, 02 and the adenylate system if the P/O ratio is 3. 

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