Electron-transport rates in enzyme

SURRIDGE ET AL. Electron- Transport Rates in Enzyme Electrode... 

A compound which is a good choice for an artificial electron relay is one which can reach the reduced FADH2 active site, undergo fast electron transfer, and then transport the electrons to the electrodes as rapidly as possible. Electron-transport rate studies have been done for an enzyme electrode for glucose (G) using interdigitated array electrodes (41). The following mechanism for redox reactions in osmium polymer—GOD biosensor films has... 

The experiments were based on the well known phenomenon that the photosynthetic electron transport gets stimulated when ADP is added to the suspension thus allowing the membranes to form ATP. The stimulated electron transport rate decreases again as soon as the added ADP is consumed. Therefore the membranes are exposed to a substrate concentration (ADP) between 0 and the concentration at the beginning of the experiment. It can be shown that the stimulation of the electron transport is proportional to the actual phosphorylation activity. This makes it possible to determine any time the ADP concentration in the cuvette, the rate of ATP synthesis and the rate of total electron transport. On this basis we have enough information to analyse the experimental reactions according to the classical enzyme kinetics as shown in Fig. 1. 

When induced in macrophages, iNOS produces large amounts of NO which represents a major cytotoxic principle of those cells. Due to its affinity to protein-bound iron, NO can inhibit a number of key enzymes that contain iron in their catalytic centers. These include ribonucleotide reductase (rate-limiting in DNA replication), iron-sulfur cluster-dependent enzymes (complex I and II) involved in mitochondrial electron transport and cis-aconitase in the citric acid cycle. In addition, higher concentrations of NO,... 

Leger C, Jones AK, Albracht SPJ, Armstrong FAA. 2002. Effect of a dispersion of interfacial electron transfer rates on steady state catalytic electron transport in [NiFe]-hydrogenase and other enzymes. J Phys Chem B 106 13058-13063. 

Reviewing the criteria for inclusion of components into the electron transport chain, Slater (1958) highlighted considerations previously advanced by H.A. Krebs as necessary to establish a pathway, namely that the amounts of enzyme present must be commensurate with enzymic activity in the preparation, activity should be fully restored by the reintroduction of the postulated component into an inhibited or depleted preparation, and that the rates of oxidation and reduction of components must be at least as great as those in the system overall. Reduction of cytochrome b by the systems then in use was thought by Chance (1952) and Slater (1958) to be too slow for the inclusion of this cytochrome into the main chain. 

The inner mitochondrial membrane can be disrupted into five sepa rate enzyme complexes, called complexes I, II, III, IV, and V. Complexes I to IV each contain part of the electron transport chain (Figure 6.8), whereas complex V catalyzes ATP synthesis (see p. 78). Each complex accepts or donates electrons to relatively mobile electron carriers, such as coenzyme Q and cytochrome c. Each car rier in the electron transport chain can receive electrons from an electron donor, and can subsequently donate electrons to the next carrier in the chain. The electrons ultimately combine with oxygen and protons to form water. This requirement for oxygen makes the electron transport process the respiratory chain, which accounts for the greatest portion of the body s use of oxygen. 

---