Shuttle transfer

Answer The malate-aspartate shuttle transfers electrons and protons from the cytoplasm into the mitochondrion. Neither NAD+ nor NADH passes through the inner membrane, thus the labeled NAD moiety of [7-14C]NADH remains in the cytosol. The 3H on [4-3H]NADH enters the mitochondrion via the malate-aspartate shuttle (see Fig. 19-29). In the cytosol, [4-3H]NADH transfers its 3H to oxaloacetate to form [3H]malate, which enters the mitochondrion via the malate-a-ketoglutarate transporter, then donates the 3H to NAD+ to form [4-3H]NADH in the matrix. 

The complete oxidation of a molecule of glucose results in the synthesis of 29.5 to 31 molecules of ATP, depending on whether the glycerol phosphate shuttle or the malate-aspar-tate shuttle transfers electrons from cytoplasmic NADH to the mitochondrial ETC. 

How do shuttle mechanisms differ from one another Two shuttle mechanisms—the glycerol—phosphate shuttle and the malate—aspartate shuttle—transfer the electrons, but not the NADH, produced in cytosolic reactions into the mitochondrion. In the hrst of the two shuttles, which is found in muscle and brain, the electrons are transferred to FAD in the second, which is found in kidney, hver, and heart, the electrons are transferred to NAD. With the malate-aspartate shuttle, 2.5 molecules of ATP are produced for each molecule of cytosolic NADH, rather than 1.5 ATP in the glycerol-phosphate shuttle, a point that affects the overall yield of ATP in these tissues. 

A9.2.2 Electric Air-controlled flute Vulve. An. electrically operated air-controlled gate valve, located between the.shuttle transfer.unit and the laboratory selector, separates the system into two sections and stops the flow of air into the laboratory while the shuttle is propelled into the reactor, irradiated, and expelled,... 

A9.2.4. Laboratory Selector. No drawings have been prepared for the laboratory selector unit as its construction will be very similar to the shuttle transfer unit. It differs only in the arrangement and number of tubes required for servicing the laboratories. The selector can be located close to the transfer unit or it can be set up at some convenient location in- the laboratory building. 

If the shuttle is to be sent to the laboratory, the shuttle transfer tube is rotated to the laboratory position during the time interval in which the shuttle is irradiated. Rotation of the shuttle transfer tube automatically closes the solenoid valve that has been supplying the air to propel and cool the shuttle and, after a fraction of a second delay, opens the solenoid valve in the air-supply line that by-passes the shuttle transfer unit. This now provides the air necessary to cool the shuttle and the shock absorber. 

One of the ways for the improvement of the positive electrode is to use a composite obtained by the impregnation of multiwall carbon nanotubes (MWNTs) by liquid sulfur. MWNTs with a high true surface area and high electron conductivity, on the one hand, promote retention of polysulfides in the positive electrode bulk (thus decreasing the shuttle transfer and self-discharge) and, on the other hand, enhance the electrode performance across its depth. 

The carbon-carbon leading edges of the shuttle transfer the aerodynamic forces to the A1 substructure and to ensure that the temperature of the A1 did not exceed 180°C, a layer of insulation was positioned between the carbon-carbon and Al. The carbon-carbon leading edge can safely withstand the impact from meteors without fracturing. 

Figure 16.2 The malate/aspartate shuttle and the 3-glycerol phosphate shuttle transfer reducing equivalents from the cytosol to the mitochondrion.

H. N. KeUey and G. L. SEAh, Assessment of Alternate Thermal Protection Systemsfor the Space Shuttle Orbiter (AIAA/ASME 3rd Joint Thermophysics, Eluids, Plasma and Heat Transfer Conference, June 7—11, 1982, St. Louis, Mo., AIAA-82-0899, 1982. 

The final step of the reaction involves the transfer of two electrons from iron-sulfur clusters to coenzyme Q. Coenzyme Q is a mobile electron carrier. Its isoprenoid tail makes it highly hydrophobic, and it diffuses freely in the hydrophobic core of the inner mitochondrial membrane. As a result, it shuttles electrons from Complexes I and II to Complex III. The redox cycle of UQ is shown in Figure 21.5, and the overall scheme is shown schematically in Figure 21.6. 

In the glycerophosphate shuttle, two different glycerophosphate dehydrogenases, one in the cytoplasm and one on the outer face of the mitochondrial inner membrane, work together to carry electrons into the mitochondrial matrix (Figure 21.32). NADH produced in the cytosol transfers its electrons to dihydroxyaeetone phosphate, thus reducing it to glyeerol-3-phosphate. This metabolite is reoxidized by the FAD -dependent mitochondrial membrane enzyme to... 

Figure 25 Schematic diagram of an injection/transfer molding machine [9]. (a) Hydraulic separation unit for upper mold plate, (b) Hydraulic separation unit for middle mold plate, (c) Shuttle system with automatic sprue nipple removal, (d) Brushing unit for cleaning middle mold plate, (e) Hydraulic ejector for automatic ejection.

Further improvements can be achieved by replacing the oxygen with a non-physiological (synthetic) electron acceptor, which is able to shuttle electrons from the flavin redox center of the enzyme to the surface of the working electrode. Glucose oxidase (and other oxidoreductase enzymes) do not directly transfer electrons to conventional electrodes because their redox center is surroimded by a thick protein layer. This insulating shell introduces a spatial separation of the electron donor-acceptor pair, and hence an intrinsic barrier to direct electron transfer, in accordance with the distance dependence of the electron transfer rate (11) ... 

Another pathway is the L-glycerol 3-phosphate shuttle (Figure 11). Cytosolic dihydroxyacetone phosphate is reduced by NADFl to s.n-glycerol 3-phosphate, catalyzed by s,n-glycerol 3-phosphate dehydrogenase, and this is then oxidized by s,n-glycerol 3-phosphate ubiquinone oxidoreductase to dihydroxyacetone phosphate, which is a flavoprotein on the outer surface of the inner membrane. By this route electrons enter the respiratory chain.from cytosolic NADH at the level of complex III. Less well defined is the possibility that cytosolic NADH is oxidized by cytochrome bs reductase in the outer mitochondrial membrane and that electrons are transferred via cytochrome b5 in the endoplasmic reticulum to the respiratory chain at the level of cytochrome c (Fischer et al., 1985). 

Mediated electrolyses make use of electron transfer mediators PjQ that shuttle electrons between electrodes and substrates S, avoiding adverse effects encountered with the direct heterogeneous reaction of substrates at electrode surfaces (Scheme 6). In recent years this mode of electrochemical synthesis has been widely studio and it is becoming increasingly well understood. A review is given in vol 1 of the present electrochemistry series... 

Coenzymes serve as recyclable shuttles—or group transfer reagents—that transport many substrates from their point of generation to their point of utilization. Association with the coenzyme also stabilizes substrates such as hydrogen atoms or hydride ions that are unstable in the aqueous environment of the cell. Other chemical moieties transported by coenzymes include methyl groups (folates), acyl groups (coenzyme A), and oligosaccharides (dolichol). 

Figure 12-12. Glycerophosphate shuttle for transfer of reducing equivalents from the cytosol into the...

Phase transfer catalysis (PTC) refers to the transfer of ions or organic molecules between two liquid phases (usually water/organic) or a liquid and a solid phase using a catalyst as a transport shuttle. The most common system encountered is water/organic, hence the catalyst must have an appropriate hydrophilic/lipophilic balance to enable it to have compatibility with both phases. The most useful catalysts for these systems are quaternary ammonium salts. Commonly used catalysts for solid-liquid systems are crown ethers and poly glycol ethers. Starks (Figure 4.5) developed the mode of action of PTC in the 1970s. In its most simple... 

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