In this shuttle, the enzyme called cytoplasmic glycerol-3-phosphate dehydrogenase 1 (GPD1 or cGPD) converts dihydroxyacetone phosphate (2) to glycerol 3-phosphate (1) by oxidizing one molecule of NADH to NAD as in the following reaction:
Glycerol-3-phosphate is converted back to dihydroxyacetone phosphate by an inner membrane-bound mitochondrial glycerol-3-phosphate dehydrogenase 2 (GPD2 or mGPD), this time reducing one molecule of enzyme-bound flavin adenine dinucleotide (FAD) to FADH.  FADH then reduces coenzyme Q (ubiquinone to ubiquinol) whose electrons enter into oxidative phosphorylation. This reaction is irreversible. These electrons bypass Complex I of the electron transport chain, making the glycerol-3-phosphate shuttle less energetically efficient compared to oxidation of NADH by Complex I.