The main difference between RuBisCo and PEP carboxylase is that RuBisCo is an enzyme that plays a vital role in the first major step of carbon fixation, whereas PEP carboxylase is a mesophyll cell enzyme that catalyzes carbon fixation in C4 plants.
Carbon fixation is the process by which photosynthetic organisms turn inorganic carbon into organic compounds. RuBisCo and PEP carboxylase are two enzymes that take part in the carbon fixation process in plants.
Key Areas Covered
1. What is RuBisCo
– Definition, Features
2. What is PEP Carboxylase
– Definition, Features
3. Difference Between RuBisCo and PEP Carboxylase
– Comparison of Key Differences
Key Terms
PEP Carboxylase, RuBisCo, Ribulose-1,5-bisphosphate Carboxylase Oxygenase
What is RuBisCo
RuBisCo, also known as Ribulose-1,5-bisphosphate carboxylase oxygenase, is an enzyme present in algae, plants, and some bacteria. It is the most abundant enzyme on Earth. RuBisCo takes part in the process of carbon fixation in photosynthesis. It catalyzes the carboxylation of ribulose -1,5-bisphosphate(RuBP), which is a five-carbon sugar. This means it catalyzes the addition of carbon dioxide to RuBP, which results in the formation of two molecules of 3-phosphoglycerate(3-PGA). This is the first step of the Calvin cycle. It also reacts with oxygen in photorespiration, which is a wasteful process that leads to the loss of energy and the release of carbon dioxide. But the affinity of RuBisCO is much higher for carbon dioxide than oxygen; hence photosynthesis is preferred over photorespiration.
In C3 plants, RuBisCo is present in the mesophyll cells, whereas in C4 plants, it is present in the bundle sheet cells. RuBisCO is a large complex protein with both large and small chains. It consists of 8 large chains that form 4 dimers and 8 small chains. Moreover, large chains contain the active site of the enzyme. Some bacteria and dinoflagellates have only a large subunit. The chloroplast DNA codes the large chain, while the nuclear DNA codes the small chain. The metal cation required for the activity of this enzyme is Mg2+. Additionally, the molecular weight of RuBisCo is about 540000Da.
Another feature of RuBisCo is that it is inactive in the dark and gets activated in the light. RuBisCo is activated by binding carbon dioxide and Mg2+ ions to the lysine residue near the active site. This results in conformational changes and the stability of the active form of the enzyme.
What is PEP Carboxylase
Phosphoenolpyruvate carboxylase, also called PEP carboxylase, is an enzyme belonging to the family Carboxy-lyases. They are present in plants and in some bacteria (e.g., Escherichia coli bacteria) that catalyze the addition of bicarbonate to phosphoenolpyruvate to form the four-carbon compound oxaloacetate and inorganic phosphate. PEP carboxylase is mostly present in the mesophyll cells of leaves and participates in the initial fixation of carbon dioxide during photosynthesis.
PEP carboxylase catalyzes the addition of carbon dioxide to phosphoenolpyruvate, which is a three-carbon compound. This phosphoenolpyruvate is produced during glycolysis. The reaction results in the production of oxaloacetate, which is a four-carbon compound. This four-carbon compound is an intermediate in the Krebs cycle.
Several factors, such as pH, temperature, and concentration of certain metabolites like malate and ATP,, control PEP carboxylase’s activity. It is also regulated by several transcription factors that increase or decrease the production of the enzyme in response to the changes in the environment. Hence, PEP carboxylase is a highly regulated enzyme.
Difference Between RuBisCo and PEP Carboxylase
Definition
RuBisCo is an enzyme in plants that catalyzes the first step of carbon fixation, while PEP Carboxylase is an enzyme in plants that catalyzes the fixation of carbon dioxide into organic compounds during photosynthesis.
Distribution
RuBisCo is present in all photosynthetic organisms, including plants, algae, and cyanobacteria, while PEP carboxylase is mainly present in C4 plants and in some bacteria.
Conclusion
Carbon fixation is the process by which photosynthetic organisms turn inorganic carbon into organic compounds. Both RuBisCo and PEP carboxylase are two enzymes that take part in the process of carbon fixation in plants. The main difference between RuBisCo and PEP carboxylase is that RuBisCo is an enzyme that plays a vital role in the first major step of carbon fixation, whereas PEP carboxylase is a mesophyll cell enzyme that catalyzes carbon fixation in C4 plants.
Reference:
1. “RuBisCO.” Byju’s.
2. “PEP Carboxylase.” Byju’s.
Image Courtesy:
1. “RuBisCOL2S2” (CC BY-SA 3.0) via Commons Wikimedia
2. “PEP Carboxylase Mechanism” By Tims2015 – Own work (CC BY-SA 3.0) via Commons Wikimedia
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