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Apr 20, 2020 · Shuttle Pathways or Systems. (Transport of reducing equivalents) The inner mitochondrial membrane is impermeable to NADH. NADH produced in the cytosol cannot directly enter the mitochondria. NADH produced in the glycolysis is extramitochondrial, whereas the electron transport chain, where NADH has to be oxidized to NAD+ is in the mitochondrion.
shuttle mechanisms is the transport of reducing equivalents across the mitochondrial membrane. Two separate methods are used for this purpose: the Glycerophosphate shuttle and the Malate-Aspartate shuttle.
The mitochondrial shuttles are biochemical transport systems used to transport reducing agents across the inner mitochondrial membrane. NADH as well as NAD+ cannot cross the membrane, but it can reduce another molecule like FAD and [QH 2] that can cross the membrane, so that its electrons can reach the electron transport chain.
Glycerol - phosphate shuttle is a shuttle that is used to regenerate NAD+ from NADH. NADH is a byproduct of glycolysis. NADH synthesised in the cytosol by glycolysis is transported to mitochondria to participate in the oxidative phosphorylation to generate ATP.
The malate–aspartate shuttle (sometimes simply the malate shuttle) is a biochemical system for translocating electrons produced during glycolysis across the semipermeable inner membrane of the mitochondrion for oxidative phosphorylation in eukaryotes.
This shuttle system (Figure 21.19) relies on redox interconversions of malate and oxaloacetate. In the cytosol, NADH reduces oxaloacetate to malate and then malate is transported into the mitochondrion by a specific transporter protein.
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Figure\(\PageIndex{13}\): The Malate-Aspartate Shuttle System. Once oxaloacetate has been effectively transported via the Malate-Aspartate Shuttle into the cytoplasm, it is converted to phosphoenolpyruvate (PEP) by the PEP carboxykinase (PEPCK).
