Question

Describe the malate shuttle system. How does it work? Why is it needed?

Answer 1

Malate shuttle system is also called as Malate aspartate shuttle . It is a very important mechanism in mitochondria which is needed to translocate electrons to move across the impermeable membrane between cytosol and mitochondrial matrix.

The electrons are released during glycolysis and it cross the membrane as it is needed in oxidative phosphorylation and then enter the electron transport chain(ETC) of mitochondria. As the inner membrane of the mitochondria are not permeable to primary reducing equivalent NADH of Electron transport chain , malate carries this equivalent across the membrane.

Cytosol Malate dehydrogenase catalyses oxaloacetate and NADH to produce malate and NAD+ in cytosol. Then the first antiporter, malate alpha ketoglutarate imports this malate into the mitochondrial matrix and the mitochondrial malate dehydrogenase convert this malate into oxaloacetate and NADH . Oxaloacetate is then converted to aspartate by aspartate aminotransferase .

The second antiporter , glutamate aspartate imports glutamate from cytosol into matrix and exports aspartate from matrix to cytosol.The NADH in the matrix helps to move the electrons to ETC for ATP synthesis.