Glycerol phosphate shuttle


The glycerol-3-phosphate shuttle is a mechanism that regenerates NAD+ from NADH, a by-product of glycolysis. 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 converts dihydroxyacetone phosphate to glycerol 3-phosphate 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, this time reducing one molecule of enzyme-bound flavin adenine dinucleotide to FADH2. FADH2 then reduces coenzyme Q 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.