The mitochondrial shuttles are systems used to transport reducing agents across the inner mitochondrial membrane. NADH and FADH2 cannot cross the membrane, but they can reduce other molecules which can cross the membrane. Inside, those molecules then regenerate NADH or FADH.
The two main systems in humans are:
|Name||In, to mitochondrion||To ETC||Out, to cytosol|
|Glycerol phosphate shuttle||glycerol 3-phosphate||FADH2 (=2 ATP)||dihydroxyacetone phosphate|
|Malate-aspartate shuttle||malate||NADH (=3 ATP)||oxaloacetate/aspartate|
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