Glycerol-3-Phosphate Shuttle

Notes

Located: Brain + skeletal muscle

This shuttle uses DHAP (from glycolysis) and converts it into glycerol-3-phosphate. It does this by taking a H+ and electrons from NADH (converting it to NAD+) to put on glycerol-3-phosphate. 

Enzyme: Cytoplasmic glycerol-3-phosphate dehydrogenase 

The glycerol-3-phosphate is then free to enter the outer mitochondrial membrane and reaches the inner mitochondrial membrane where it gets reduced, losing the e- and H+ ions, returning it to DHAP to return to the cytosol. The electrons and H+ interact with FAD to form FADH2, which gets transferred onto coenzyme Q to make QH2. 

This then proceeds down the ETC to pump H+. 

Due to the fact that this enters at Complex II, there is a loss of proton pumping that could have occured at Complex I. 

Therefore, this system has a lower ATP yield than the malate-aspartate shuttle! 

Why is this system used?

This system is used because brain and skeletal muscles need energy quickly. While it is not the most efficient, the energy demands are high so a quicker production rate works better, rather than a longer wait time but higher payoff.