The main difference between malate-aspartate shuttle and glycerol-3-phosphate shuttle is that malate-aspartate shuttle is mainly used in high-energy demand tissues, whereas glycerol-3 phosphate is used in tissues with low energy demands.
Malate aspartate shuttle and glycerol-3-phosphate shuttle are mechanisms that allow the transfer of reducing equivalents, especially NADH, from the cytosol into the mitochondria for ATP synthesis. These substances differ in their distinct mechanisms of action and the specific types of cells on which they act.
Key Areas Covered
1. What is Malate-Aspartate Shuttle
– Definition, Features, Uses
2. What is Glycerol-3-Phosphate Shuttle
– Definition, Features, Uses
3. Difference Between Malate-Aspartate Shuttle and Glycerol-3-Phosphate Shuttle
– Comparison of Key Differences
Key Terms
Malate-Aspartate Shuttle, Glycerol-3-Phosphate Shuttle
What is Malate-Aspartate Shuttle
Malate aspartate shuttle is a mechanism that allows the transfer of reducing equivalents, specifically NADH, from the cytosol into the mitochondria for ATP synthesis. This shuttle is mainly used in the high energy demand tissues such as heart and liver cells.
The malate aspartate shuttle comprises several enzymes and transporters that function together to facilitate the transfer of reducing equivalents from the cytosol into the mitochondria. The enzyme malate dehydrogenase oxidizes cytosolic NADH, producing malate, which is transported into the mitochondria via a malate transporter, initiating the first step of the reaction. Within the mitochondria, malate dehydrogenase then oxidizes malate back into NADH, generating NAD+ and producing oxaloacetate. This oxaloacetate is subsequently transaminated into aspartate, which is transported out of the mitochondria and back into the cytosol. The cytosol deaminates aspartate, producing oxaloacetate, which is useful in the citric acid cycle for ATP generation. This is the mechanism of the malate aspartate shuttle.
The physiological significance of the malate aspartate shuttle involves maintaining the energy balance in cells with high energy demands, such as heart and liver cells.
What is Glycerol-3-Phosphate Shuttle
The glycerol-3 phosphate shuttle involves the transfer of reducing equivalents from the cytosol into the mitochondria for ATP synthesis. In the first step of the glycerol-3-phosphate shuttle, which occurs in the cytosol, NADH is oxidized by GPDH to produce glycerol-3-phosphate and NAD+. This glycerol-3-phosphate diffuses across the mitochondrial membrane and enters the mitochondrial matrix. Then, in the matrix, FAD-GPDH oxidizes glycerol-3-phosphate to produce FADH2 and dihydroxyacetone phosphate. FADH2 then donates electrons to the electron transport chain, which results in the production of ATP.
Moreover, the glycerol-3-phosphate shuttle plays an important role in cellular metabolism and energy production. In muscle cells, the glycerol-3-phosphate shuttle is responsible for the production of ATP during periods of high energy demand. In neurons, the glycerol-3-phosphate shuttle is responsible for the production of ATP necessary for neurotransmitter release. The glycerol-3-phosphate shuttle also involves in the regulation of cellular metabolism.
Difference Between Malate-Aspartate Shuttle and Glycerol-3-Phosphate Shuttle
Definition
Malate aspartate shuttle is a mechanism that allows the transfer of reducing equivalents, specifically NADH, from the cytosol into the mitochondria for ATP synthesis. On the other hand, the glycerol-3 phosphate shuttle is a mechanism that involves the transfer of reducing equivalents from the cytosol into the mitochondria for ATP synthesis through a series of enzymatic reactions involving the oxidation of cytosolic NADH by glycerol-3-phosphate dehydrogenase and the transport of glycerol-3-phosphate into the mitochondria for further processing.
Enzymes Used
Malate aspartate shuttle uses malate dehydrogenase and aspartate aminotransferase, while glycerol -3-phosphate shuttle uses glycerol-3-phosphate dehydrogenase and FAD independent glycerol-3-phosphate dehydrogenase.
Use
The malate-aspartate shuttle is mainly used in high-energy demand tissues, whereas glycerol-3 phosphate is used in tissues with low energy demands.
ATP Yield
Malate-aspartate shuttle produces 2.5 ATP per electron pair transferred, while the glycerol-3-phosphate shuttle produces 1.5 ATP per electron pair transferred.
Efficiency
The malate-aspartate shuttle is more efficient than the glycerol-3-phosphate shuttle.
Conclusion
In brief, the malate-aspartate shuttle and the glycerol-3-phosphate shuttle are mechanisms that allow the transfer of reducing equivalents, specially NADH, from the cytosol into the mitochondria for ATP synthesis. The main difference between malate-aspartate shuttle and glycerol-3-phosphate shuttle is that the malate-aspartate shuttle is mainly useful in high-energy demand tissues, whereas glycerol-3 phosphate is useful in tissues with low energy demands.
Reference:
1. “Pathway: glycerol-3-phosphate shuttle.” MetaCYC.org
2. “Malate-Aspartate Shuttle.” PubChem. National Library of Medicine.
Image Courtesy:
1. “Malate-aspartate shuttle” By Yikrazuul – Own work; PMID 17237342 (CC BY-SA 3.0) via Commons Wikimedia
2. “Glycerol-3-phosphate shuttle” By Curtis Neveu – created this work by myself. (CC BY-SA 3.0) via Commons Wikimedia
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