Pep carboxylase

Definition

Pep carboxylase, also known as phosphoenolpyruvate carboxylase (PEPC), is an enzyme that catalyzes the addition of carbon dioxide to phosphoenolpyruvate (PEP) to form oxaloacetate. This enzyme plays a crucial role in C4 and CAM pathways of photosynthesis, enabling plants to efficiently fix carbon in conditions where traditional Calvin cycle fixation would be less effective.

5 Must Know Facts For Your Next Test

1. Pep carboxylase is primarily found in mesophyll cells of C4 plants and in the stomata of CAM plants, making it essential for their carbon fixation processes.
2. This enzyme operates optimally at high temperatures and low concentrations of CO2, which allows C4 and CAM plants to thrive in arid conditions.
3. Unlike ribulose bisphosphate carboxylase (RuBisCO), which is the primary carbon-fixing enzyme in the Calvin cycle, pep carboxylase does not catalyze oxygenation reactions, thus avoiding photorespiration.
4. The activity of pep carboxylase is regulated by factors such as pH and the presence of certain ions, which can influence its efficiency and activity.
5. In C4 plants, pep carboxylase helps concentrate CO2 in bundle sheath cells, facilitating more efficient photosynthesis under conditions of high light intensity and temperature.

Review Questions

• How does pep carboxylase contribute to the efficiency of carbon fixation in C4 and CAM plants?
  • Pep carboxylase enhances carbon fixation efficiency in C4 and CAM plants by catalyzing the conversion of phosphoenolpyruvate to oxaloacetate with the incorporation of CO2. This reaction occurs in mesophyll cells for C4 plants or during nighttime in CAM plants, allowing these species to capture carbon effectively even under low CO2 conditions or high temperatures. By utilizing this enzyme, these plants minimize the negative effects of photorespiration that often occurs with RuBisCO.
• Discuss the differences between pep carboxylase and RuBisCO regarding their roles in plant photosynthesis.
  • Pep carboxylase and RuBisCO serve different functions in plant photosynthesis. Pep carboxylase fixes CO2 into a four-carbon compound while operating mainly in C4 and CAM pathways, thus avoiding photorespiration. In contrast, RuBisCO is central to the Calvin cycle, fixing CO2 into a five-carbon sugar but can also catalyze oxygenation reactions that lead to photorespiration. The efficiency of pep carboxylase in high temperatures and low CO2 concentrations makes it more suitable for arid environments than RuBisCO.
• Evaluate the ecological significance of pep carboxylase's role in C4 and CAM photosynthesis as compared to traditional C3 photosynthesis.
  • The ecological significance of pep carboxylase lies in its ability to support plant survival in extreme conditions, such as high temperatures and droughts. By enabling C4 and CAM plants to efficiently fix carbon dioxide even when it is scarce, these pathways allow such plants to conserve water while maximizing photosynthesis. In contrast, traditional C3 photosynthesis relies heavily on RuBisCO, which can lead to increased rates of photorespiration under stress. Thus, pep carboxylase's function allows C4 and CAM plants to occupy niches where C3 plants would struggle, promoting biodiversity and ecosystem resilience.

Related terms

Phosphoenolpyruvate (PEP): A key intermediate in glycolysis and a four-carbon compound that serves as the substrate for pep carboxylase.

Oxaloacetate: A four-carbon dicarboxylic acid that is formed from the reaction between CO2 and PEP, playing a significant role in metabolic pathways.

C4 Photosynthesis: A photosynthetic pathway that uses pep carboxylase to fix carbon dioxide into a four-carbon compound, enhancing efficiency in hot and dry environments.