The most active NADH shuttle, which functions in liver, kidney, and heart mitochondria, is the malate-aspartate shuttle. The cytosolic reducing equivalents of NADH are first transferred to the cytosolic oxaloacetate to yield malate, and this is catalysed by cytosolic malate dehydrogenase. The malate thus formed passes through the inner membrane via the malate–ketoglutarate transporter. Within the matrix,…

The NADH dehydrogenase of the inner mitochondrial membrane of animal cells can accept electrons only from NADH in the matrix. The inner membrane is not permeable to NADH. This has to be reoxidised to NAD+ by O2 via the respiratory chain. This can be overcome by the special shuttle systems carry reducing equivalents from cytosolic NADH into…

This is the second membrane system functioning in oxidative phosphorylation. It promotes transport of  along with that of H+ from the cytosol into the matrix compartments as the entrance of the inorganic phosphate is coupled to the entrance of H+. This system is aptly designated as Pi-H+ symporter. The phosphate translocase system is specific for phosphate. Thus, the…

This system consists of a specific protein that extends across the inner membrane. It trans-locates one molecule of ADP inward in exchange for one molecule of ATP4-coming out. As the entrance of ADP is coupled to the exit of ATP, this system is better called ADP-ATP antiporter. Obviously, this transport system is moving more negative…

The mitochondrial outer membrane is freely permeable to most small solute molecules, but the inner membrane is impermeable to H+, OA−, K+, and also many other ionic solutes. How, then, can the ADP3 and  produced in the cytosol enter the matrix and how can the newly formed ATP4− leave again, since oxidative phosphorylation takes place within the inner…

According to Mitchell, the respiratory chain is folded into three oxidation reduction loops (o/r loops) as shown in Figure 8.24. Each pair of electrons transferred from NADH to oxygen causes six protons to be translocated from inside to outside of the membrane. NADH first donates one H+ and two electrons, which together with another H+ from the internal…

Mitchell has explained the concept based on the fact that the reducing equivalents are transferred as H atoms by electron carriers (ubiquinone) and others (such as Fe-S centre and cytochrome). He explained that the hydrogen- and electron-carrying proteins are present in alternate in the respiratory chain to form three functional loops called the oxidation–reduction loops…

The inhibitors involved in the electron transport arrest respiration by combing with membranes of the respiratory chain rather than with the enzymes that are involved in coupling respiration with ATP synthesis. They appear to act at three loci that may be identical to the energy transfer sites I, II, and III as stated in the…

The inhibitors bind to one of the components of ETC and block the transport of electrons. This causes the accumulation of reduced components before the inhibitor blockade step and oxidised components after the inhibitor step. The synthesis of ATP (phosphorylation) depends on electron transport. Hence, all the site-specific inhibitors of ETC also inhibit ATP formation.…

Salient features This is a simpler, radically different, and novel mechanism and was postulated by Peter Mitchell, a British biochemist in 1961. He proposed that “electron transport and ATP synthesis are coupled to high-energy intermediate or an activated protein” as shown in Figure 8.23. According to this model, the transfer of electrons through the respiratory chain…