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The glycerol-3-phosphate shuttle is a mechanism that regenerates NAD+ from
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
The glycerol-3-phosphate shuttle is a mechanism that regenerates NAD+ from NADH
Nicotinamide adenine dinucleotide (NAD) is a coenzyme central to metabolism. Found in all living cells, NAD is called a dinucleotide because it consists of two nucleotides joined through their phosphate groups. One nucleotide contains an aden ...
, a by-product of glycolysis. The shuttle consists of the sequential activity of two proteins: GPD1 which transfers an electron pair from NADH to dihydroxyacetone phosphate (DHAP), forming glycerol-3-phosphate (G3P) and regenerating NAD+ needed to generate energy via glycolysis. The mitochondrial inner membrane protein GPD2 catalyzes the oxidation of G3P, regenerating DHAP in the cytosol and forming FADH2 in the mitochondrial matrix. In mammals, its activity in transporting reducing equivalents across the mitochondrial membrane is considered secondary to the malate-aspartate shuttle.
History
The glycerol phosphate shuttle was first characterized as a major route of mitochondrial hydride transport in the flight muscles of blow flies. It was initially believed that the system would be inactive in mammals due to the predominance oflactate dehydrogenase
Lactate dehydrogenase (LDH or LD) is an enzyme found in nearly all living cells. LDH catalyzes the conversion of lactate to pyruvate and back, as it converts NAD+ to NADH and back. A dehydrogenase is an enzyme that transfers a hydride from one ...
activity over Glycerol-3-phosphate dehydrogenase 1 (GPD1) until high GPD1 and GPD2 activity were demonstrated in mammalian brown adipose tissue
Brown adipose tissue (BAT) or brown fat makes up the adipose organ together with white adipose tissue (or white fat). Brown adipose tissue is found in almost all mammals.
Classification of brown fat refers to two distinct cell populations with si ...
and pancreatic ß-islets.
Reaction
In this shuttle, the enzyme called cytoplasmic glycerol-3-phosphate dehydrogenase 1 (GPD1 or cGPD) convertsdihydroxyacetone phosphate
Dihydroxyacetone phosphate (DHAP, also glycerone phosphate in older texts) is the anion with the formula HOCH2C(O)CH2OPO32-. This anion is involved in many metabolic pathways, including the Calvin cycle in plants and glycolysis.Nelson, D. L.; C ...
(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
Flavin may refer to:
Placename
* Flavin, Aveyron, a commune in southern France
Surname
* Adrian Flavin (born 1979), a professional rugby player
* Christopher Flavin, president of the Worldwatch Institute
* Dan Flavin (1933–1996), a minimali ...
(FAD) to FADH2. FADH2 then reduces coenzyme Q
Coenzyme Q, also known as ubiquinone and marketed as CoQ10, is a coenzyme family that is ubiquitous in animals and most bacteria (hence the name ubiquinone). In humans, the most common form is coenzyme Q10 or ubiquinone-10.
It is a 1,4-benzoq ...
(ubiquinone to ubiquinol) whose electrons enter into oxidative phosphorylation
Oxidative phosphorylation (UK , US ) or electron transport-linked phosphorylation or terminal oxidation is the metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing chemical energy in order to produce adenosine t ...
. This reaction is irreversible.
See also
* Malate-aspartate shuttle * Mitochondrial shuttleReferences
External links
* http://chemistry.elmhurst.edu/vchembook/601glycolysissum.html (describes the shuttle in the context of glycolysis) Cellular respiration {{biochemistry-stub