What is malate aspartate shuttle?

The malate aspartate shuttle is a biochemical process that occurs in the mitochondria of cells and plays a crucial role in transporting reducing equivalents (such as NADH) from the cytoplasm into the mitochondria.

In this shuttle, NADH produced in glycolysis is not able to directly enter the mitochondrial matrix, where it is needed for oxidative phosphorylation. Instead, NADH is used to reduce oxaloacetate to malate in the cytoplasm. Malate is then transported into the mitochondria, where it is oxidized back to oxaloacetate by malate dehydrogenase. This reaction regenerates NADH, which can then be used in the electron transport chain.

The newly formed oxaloacetate is then transaminated to aspartate by aspartate aminotransferase, forming α-ketoglutarate. The aspartate is transported back to the cytoplasm, where it can be deaminated to form oxaloacetate, allowing the shuttle to continue.

The malate aspartate shuttle is an essential process for maintaining the balance of reducing equivalents in the cell and ensuring the efficient production of ATP through oxidative phosphorylation. It is particularly important in tissues with high energy demands, such as skeletal muscle and the heart.