![]() ![]() Evidence of highly regulated malate-aspartate shuttle in adult human brain has been documented. The activity of the malate-aspartate shuttle increases during development in parallel with synaptogenesis, which is consistent with the high activity and importance of this shuttle in neurons and synaptic terminals. The electrogenic exchange of aspartate for glutamate and a. This shuttle involves both the cytosolic and mitochondrial forms of aspartate aminotransferase and malate dehydrogenase, the mitochondrial aspartate-glutamate carrier and the dicarboxylic acid carrier in brain (Fig. The malate-aspartate shuttle is the most important pathway for transferring reducing equivalents from the cytosol to the mitochondria in brain. The malate-aspartate shuttle has a role in linking metabolic pathways in brain 542. The malate-aspartate shuttle is the most important pathway for transferring reducing equivalents from the cytosol to the mitochondria in brain 541. THE MALATE-ASPARTATE SHUTTLE HAS A KEY ROLE IN BRAIN METABOLISM 541. The MALATE-ASPARTATE SHUTTLE gets reducing equivalents (electrons) from cytosolic NADH into the mitochondria so that 3 ATPs can be made. In white muscle, the a- glycerol phosphate shuttle predominates (Fig. ![]() In red muscle, heart, and brain tissues the malate-aspartate shuttle is the major pathway for shuttling electrons into mitochondria. The advantage of this shuttle is that it gives you 3 ATPs for the oxidation of each cytoplasmic NADH. The other shuttle is the malate-aspartate shuttle. Įlectrons from NADH outside the mitochondria are transported into the mitochondria by the malate-aspartate shuttle or the a- glycerol phosphate shuttle. Įlectrogenic antiport, can only operate in the direction of aspartate efflux as import of H is a requirement for the malate/aspartate shuttle. Oxidation of 2 molecules each of isocitrate, n-ketoglutarate, and malate yields 6 NADH Oxidation of 2 molecules of succinate yields 2 Oxidative phosphorylation (mitochondria) 2 NADH from glycolysis yield 1.5 ATP each if NADH is oxidized by glycerol-phosphate shuttle 2.5 ATP by malate-aspartate shuttle + 3 + 5. Most of the ATP-26 out of 30 or 28 out of 32-is produced by oxidative phosphorylation only 4 ATP molecules result from direct synthesis during glycolysis and the TCA cycle. On the other hand, if these 2 NADH take part in the malate-aspartate shuttle, each yields 2.5 ATP, giving a total (in this case) of 32 ATP formed per glucose oxidized. īecause the 2 NADH formed in glycolysis are transported by the glycerol phosphate shuttle in this case, they each yield only 1.5 ATP, as already described. MALATE ASPARTATE SHUTTLE FULLBecause this shuttle produces NADH in the matrix, the full 2.5 ATPs per NADH are recovered. In contrast to the glycerol phosphate shuttle, the malate-aspartate cycle is reversible, and it operates as shown in Figure 21.34 only if the NADH/NAD ratio in the cytosol is higher than the ratio in the matrix. Transamination in the cytosol recycles aspartate back to oxaloacetate. The oxaloacetate produced in this reaction cannot cross the inner membrane and must be transaminated to form aspartate, which can be transported across the membrane to the cytosolic side. This mitochondrial NADH readily enters the electron transport chain. Malate is transported across the inner membrane, where it is reoxidized by malate dehydrogenase, converting NAD to NADH in the matrix. Oxaloacetate is reduced in the cytosol, acquiring the electrons of NADH (which is oxidized to NAD ). The second electron shuttle system, called the malate-aspartate shuttle, is shown in Figure 21.34. ![]()
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