What is the Difference Between Malate-Aspartate Shuttle and Glycerol-3-Phosphate Shuttle

The key difference between malate-aspartate shuttle and glycerol-3-phosphate shuttle is that the malate-aspartate shuttle is a very efficient transport mechanism for NADH electrons generated in glycolysis to enter the mitochondria for use in the electron transport chain while the glycerol-3-phosphate shuttle is a less efficient transport mechanism for NADH electrons generated in glycolysis to enter the mitochondria for use in the electron transport chain.

Cellular respiration is a metabolic process that uses biological fuel known as glucose to produce adenosine triphosphate (ATP). It mainly consists of three steps: glycolysis, Kreb cycle, and electron transport chain. Transferring NADH electrons generated in the cytosol to the mitochondrial inner membrane for use in the electron transport chain is a critical process. Thus, malate-aspartate and glycerol-phosphate shuttles serve as vital transport mechanisms, facilitating the entry of NADH electrons generated during glycolysis into the mitochondria. However, the malate-aspartate shuttle is very useful in high-energy-demand tissues, while the glycerol-3 phosphate shuttle is very useful in low-energy-demand tissues.

1. Overview and Key Difference
2. What is Malate-Aspartate Shuttle
3. What is Glycerol-3-Phosphate Shuttle
4. Similarities – Malate-Aspartate Shuttle and Glycerol-3-Phosphate Shuttle
5. Malate-Aspartate Shuttle vs Glycerol-3-Phosphate Shuttle in Tabular Form
6. Summary – Malate-Aspartate Shuttle vs Glycerol-3-Phosphate Shuttle

What is a Malate-Aspartate Shuttle?

The malate-aspartate shuttle is a transport mechanism for NADH electrons generated during glycolysis in the cytosol to enter the mitochondria for use in the electron transport chain for energy production. These electrons usually enter the electron transport chain of the mitochondria through redox reactions to generate ATP. This transport mechanism is required because the mitochondrial inner membrane is impermeable to NADH. The shuttle consists of four protein parts, including malate dehydrogenase, aspartate aminotransferase malate-alpha-ketoglutarate antiporter, and glutamate-aspartate antiporter.

Malate-Aspartate Shuttle and Glycerol-3-Phosphate Shuttle - Side by Side Comparison

Figure 01: Malate-Aspartate Shuttle

This transport mechanism operates by converting oxaloacetate into malate using NADH and an enzyme called malate dehydrogenase (MDH) in the cytosol. The malate then enters the mitochondria and later regenerates the NADH again. At the final phase of this shuttle, oxaloacetate is transformed into aspartate via an enzyme called aspartate transaminase (AST) and exits the mitochondria. In the cytosol, aspartate again converts back into oxaloacetate again.

What is Glycerol-3-Phosphate Shuttle?

The glycerol-3-phosphate shuttle is a transport mechanism for NADH electrons generated during glycolysis in the cytosol to enter the mitochondria for use in the electron transport chain for energy production. The protein parts in this shuttle may include cytoplasmic glycerol 3 phosphate dehydrogenase 1 and mitochondrial glycerol 3 phosphate dehydrogenase 2.

Malate-Aspartate Shuttle vs Glycerol-3-Phosphate Shuttle in Tabular Form

Figure 02: Glycerol-3-Phosphate Shuttle

The glycerol-phosphate shuttle transport mechanism uses a different mechanism to transport electrons from NADH to the electron transport chain. In this transport mechanism, an enzyme called glycerol 3 phosphate dehydrogenase uses NADH to convert DHAP (dihydroxyacetone phosphate) into glycerol 3 phosphate in the cytosol. Later, at the inner mitochondrial membrane, the membrane-bound glycerol 3- phosphate dehydrogenase enzyme converts glycerol 3 phosphate back to DHAP. This reaction also generates FADH2. Ultimately, FADH2 moves its electrons to the electron transport chain through CoQ (coenzyme Q).

What are the Similarities Between Malate-Aspartate Shuttle and Glycerol-3-Phosphate Shuttle?

The malate-aspartate and glycerol-phosphate shuttles are crucial transport mechanisms for NADH electrons generated in glycolysis to enter the mitochondria for use in the electron transport chain (ETC) for energy production.
Both transport mechanisms use reduction equivalents or redox reactions to transfer electrons of NADH in the cytosol to mitochondria for the electron transport chain.
Both transport mechanisms have very important protein parts.
They are extremely important for ATP production.

What is the Difference Between Malate-Aspartate Shuttle and Glycerol-3-Phosphate Shuttle?

The malate-aspartate shuttle is a very efficient transport mechanism for NADH electrons generated in glycolysis to enter the mitochondria for use in the electron transport chain, while the glycerol-3-phosphate shuttle is a less efficient transport mechanism for NADH electrons generated in glycolysis to enter the mitochondria for use in the electron transport chain. Thus, this efficiency is the key difference between malate-aspartate shuttle and glycerol-phosphate shuttle. Furthermore, the malate-aspartate shuttle is very useful in high-energy-demand tissues, while the glycerol-3 phosphate shuttle is very useful in low-energy-demand tissues.

The infographic below presents the differences between malate-aspartate shuttle and glycerol-phosphate shuttle in tabular form for side-by-side comparison.

Summary – Malate-Aspartate Shuttle vs. Glycerol-3-Phosphate Shuttle

The malate-aspartate and glycerol-phosphate shuttles are crucial transport mechanisms for NADH electrons generated in glycolysis to enter the mitochondria for use in the electron transport chain (ETC) for energy production. The malate-aspartate shuttle is a very efficient transport mechanism, while the glycerol-phosphate shuttle is a less efficient transport mechanism. Hence, this is the key difference between malate-aspartate shuttle and glycerol-phosphate.

Reference:

1. “Malate-Aspartate Shuttle.” An Overview | ScienceDirect Topics.
2. Larsson C; Påhlman IL; Ansell R; Rigoulet M; Adler L; Gustafsson L; “The Importance of the Glycerol 3-Phosphate Shuttle during Aerobic Growth of Saccharomyces Cerevisiae.” Yeast (Chichester, England), U.S. National Library of Medicine.

Image Courtesy:

1. “Malateasparateshuttle” By WikipedianProlific at the English-language Wikipedia (CC BY-SA 3.0) via Commons Wikimedia
2. “Glycerol-3-phosphate shuttle” By Curtis Neveu – I created this work entirely by myself (CC BY-SA 3.0) via Commons Wikimedia