The main difference between fumarate reductase and succinate dehydrogenase is that succinate dehydrogenase enzyme catalyzes the conversion of succinate to fumarate by removing two hydrogen atoms from succinate, whereas fumarate reductase catalyzes the reverse reaction, converting fumarate back to succinate.
Fumarate reductase and succinate dehydrogenase are two enzymes that are closely related in function. They both play essential roles in cellular respiration, particularly in the citric acid cycle and the electron transport chain.
Key Areas Covered
1. What is Fumarate Reductase
– Definition, Features, Role
2. What is Succinate Dehydrogenase
– Definition, Features, Role
3. Similarities Between Fumarate Reductase and Succinate Dehydrogenase
– Outline of Common Features
4. Difference Between Fumarate Reductase and Succinate Dehydrogenase
– Comparison of Key Differences
Key Terms
Fumarate Reductase, Succinate Dehydrogenase
What is Fumarate Reductase
Fumarate reductase is a multi-subunit protein complex composed of multiple polypeptide chains. While the exact composition can vary among different species, a typical fumarate reductase consists of several essential subunits. This subunit contains heme groups and is responsible for transferring electrons within the enzyme complex. These clusters are crucial electron carriers within the enzyme, facilitating the transfer of electrons from donors to fumarate. FAD is a co-factor that participates in electron transfer. This site is responsible for binding reduced quinone (usually ubiquinone or menaquinone), which serves as the initial electron donor to the enzyme. Fumarate reductase also contains binding sites for other co-factors and substrates involved in the catalytic process.
Figure 1: Fumarate Reductase
The primary function of fumarate reductase is to catalyze the reduction of fumarate to succinate. This chemical reaction involves the addition of two electrons and two protons (2H) to fumarate, resulting in the conversion of fumarate to succinate:
Fumarate + 2H → Succinate
In this process, the electrons and protons are typically provided by reduced quinone (ubiquinol or menaquinol), which donates its electrons to the enzyme.
Role of Fumarate Reductase
Fumarate reductase activity is observed in many gut bacteria. It enables them to utilize available substrates efficiently and contribute to the fermentation processes in the digestive tract. Fumarate reductase is crucial for the microbial community to derive energy from organic matter sinking to the ocean floor in the oxygen-depleted layers of ocean sediments. Moreover, fumarate-reducing microorganisms play a role in soil ecosystems, particularly in anaerobic microsites, where they participate in carbon cycling and nutrient transformations. Fumarate reductase also has applications in bioremediation, as it can be harnessed to degrade various organic contaminants under anaerobic conditions.
What is Succinate Reductase
Succinate reductase is an enzyme complex found in the inner mitochondrial membrane. In general, succinate reductase consists of four main subunits.
Flavoprotein Subunit (SDHA): This subunit contains flavin adenine dinucleotide (FAD) and an iron-sulfur (Fe-S) cluster, both of which play crucial roles in electron transfer within the enzyme complex.
Iron-Sulfur Subunit (SDHB): This subunit contains additional Fe-S clusters and serves as an electron carrier, shuttling electrons between the flavoprotein subunit and the other components of the complex.
Cytochrome b Subunit (SDHC): This subunit contains heme groups and functions as a mediator for electron transfer between the iron-sulfur subunit and the final electron acceptor, typically ubiquinone (coenzyme Q).
Membrane Anchor Subunit (SDHD): This subunit anchors the complex to the inner mitochondrial membrane in eukaryotic cells or the plasma membrane in prokaryotes.
Succinate reductase is primarily responsible for the oxidation of succinate to fumarate in the citric acid cycle (Krebs cycle). This enzymatic reaction involves the transfer of electrons from succinate to an electron carrier, typically flavin adenine dinucleotide (FAD), resulting in the conversion of succinate to fumarate:
Succinate + FAD → Fumarate + FADH₂
FADH₂, the reduced form of FAD, subsequently donates its electrons to the electron transport chain (ETC) for further energy generation.
Figure 2: Succinate Dehydrogenase
Role of Succinate Reductase
In the electron transport chain, succinate reductase serves as Complex II, which participates in the transfer of electrons from succinate to ubiquinone (coenzyme Q), a mobile electron carrier within the inner mitochondrial membrane. This electron transfer from succinate to ubiquinone generates a proton gradient across the membrane, contributing to the proton motive force (PMF) used to generate ATP.
Succinate reductase bridges the gap between the citric acid cycle (Krebs cycle) and the electron transport chain (ETC). It directly links the oxidation of succinate to the generation of electron carriers, which are crucial for ATP production.
Through its role in the ETC, succinate reductase contributes to the generation of ATP, the primary energy currency of cells. The electrons transferred through the ETC ultimately drive the proton motive force (PMF) required for ATP synthesis.
In eukaryotic cells, succinate reductase is located in the inner mitochondrial membrane. Its proper function is essential for mitochondrial respiration and energy production.
The activity of succinate reductase is tightly regulated to ensure efficient energy production while preventing excessive accumulation of metabolic intermediates. This regulation is critical for overall metabolic homeostasis.
Dysregulation or mutations in succinate reductase subunits can lead to various metabolic disorders and diseases. For example, mutations in SDH genes have been associated with hereditary paragangliomas and pheochromocytomas, rare neuroendocrine tumors.
Similarities Between Fumarate Reductase and Succinate Dehydrogenase
- Both enzymes are involved in the conversion of organic compounds in the citric acid cycle (Krebs cycle).
- Both enzymes are involved in the transfer of electrons during these reactions.
Difference Between Fumarate Reductase and Succinate Dehydrogenase
Definition
Fumarate reductase is an enzyme that catalyzes the conversion of fumarate to succinate, playing a role in anaerobic respiration in certain microorganisms, while succinate dehydrogenase is an enzyme complex found in the inner mitochondrial membrane.
Function
Succinate dehydrogenase catalyzes the oxidation of succinate to fumarate by removing two electrons and two protons from succinate. Furthermore, this reaction involves the transfer of electrons to FAD, forming FADH₂. Meanwhile, fumarate reductase catalyzes the reverse reaction, converting fumarate back to succinate by adding two electrons and two protons to fumarate. It generally uses electrons from reduced quinone (ubiquinol or menaquinol).
Found in
Fumarate reductase is mainly found in the membranes of certain bacteria and archaea, and it can also be found in the mitochondria of some parasitic protists. Succinate dehydrogenase is found in the inner mitochondrial membrane of eukaryotic cells, specifically within the mitochondria. Moreover, in prokaryotic cells, it is located in the plasma membrane.
Conclusion
The main difference between fumarate reductase and succinate dehydrogenase is that succinate dehydrogenase enzyme catalyzes the conversion of succinate to fumarate by removing two hydrogen atoms from succinate, whereas fumarate reductase catalyzes the reverse reaction, converting fumarate back to succinate.
Reference:
1. “Succinate Dehydrogenase.” Wikipedia. Wikipedia Foundation.
2. “Fumarate Reductase.” Wikipedia. Wikipedia Foundation.
Image Courtesy:
1. “SuccDeh” By Johnhfst at English Wikipedia – Transferred from en. Wikipedia to Commons. (Public Domain) via Commons Wikimedia
2. “QFR Crystal” By AlliKeys183 – Own work (CC BY-SA 4.0) via Commons Wikimedia
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