Mitochondrial shuttle

The mitochondrial shuttles are systems used to transport reducing agents across the inner mitochondrial membrane. NADH cannot cross the membrane, but it can reduce another molecule that can cross the membrane, so that its electrons can reach the electron transport chain.

The two main systems in humans are:

Name	In, to mitochondrion	To ETC	Out, to cytosol
Glycerol phosphate shuttle	glycerol 3-phosphate	QH2 (~2 ATP)	dihydroxyacetone phosphate
Malate-aspartate shuttle	malate	NADH (~3 ATP)	oxaloacetate[1]/aspartate

In humans, the glycerol phosphate shuttle is primarily found in brown adipose tissue, as the conversion is less efficient, thus generating heat, which is one of the main purposes of brown fat. It is primarily found in babies, though it is present in small amounts in adults around the kidneys and on the back of our necks.^[1] The malate-aspartate shuttle is found in much of the rest of the body.

Notes and references

1. ^ ^{a b} Silva, Pedro. "The chemical logic behind... Fermentation and Respiration", Universidade Fernando Pessoa, 2002-01-04. Retrieved on 2009-04-02.