Glycerol phosphate shuttle
The glycerol-3-phosphate shuttle is a mechanism that regenerates NAD+ from NADH, a by-product of glycolysis. GPD1 is a gene that codes for proteins responsible for converting dihydroxyacetone phosphate and NADH to glycerol-3-phosphate and NAD+ in order to conduct bodily metabolic processes. The gene GPD2 is responsible for the reverse reaction.  Its importance in transporting reducing equivalents is secondary to the malate-aspartate shuttle.

Reaction
In this shuttle, the enzyme called cytoplasmic glycerol-3-phosphate dehydrogenase 1 (GPDH-C) converts dihydroxyacetone phosphate (2) to glycerol 3-phosphate (1) by oxidizing one molecule of NADH to NAD+ as in the following reaction:

Reverse path
Glycerol-3-phosphate gets converted back to dihydroxyacetone phosphate by an inner membrane-bound mitochondrial glycerol-3-phosphate dehydrogenase 2 (GPDH-M), this time reducing one molecule of enzyme-bound flavin adenine dinucleotide (FAD) to FADH2.  FADH2 then reduces coenzyme Q (ubiquinone to ubiquinol) which enters into oxidative phosphorylation. This reaction is irreversible.

Function
The glycerol-3-phosphate shuttle allows the NADH synthesized in the cytosol by glycolysis to contribute to the oxidative phosphorylation pathway in the mitochondria to generate ATP. It has been found in animals, fungi, and plants. Furthermore, on fungi, it was uncertain how glycerol-3-phosphate shuttle affects poisoned fungi. That was until a 2018 study by researchers Yongkai Shi, Huan Wang, Yuxin Yan, Huojuan Cao, Xiaohong Liu, Fucheng Lin, and Jianping Lu, shows that when glycerol-3-phosphate dehydrogenases 1 and 2 are removed from Pyricularia oryzae, it reduces its venom. These enzymes aid in the glycerol-3-phosphate shuttle which is involved in fungal development. Their removal hinders the process.

See also
 Malate-aspartate shuttle
 Mitochondrial shuttle

References

External links
 http://chemistry.elmhurst.edu/vchembook/601glycolysissum.html (describes the shuttle in the context of glycolysis)

Cellular respiration