What is the reaction catalysed by PEP carboxylase?

An enzyme in the carboxylases responsible for the formation of the four-carbon compound oxaloacetate by catalyzing the binding of one molecule of carbon dioxide to the three-carbon compound phosphoenolpyruvate.

Does PEP carboxylase replace Rubisco?

C4 plants use this 4-carbon compound to effectively “concentrate” CO2 around rubisco, so that rubisco is less likely re react with O2. This enzyme is called phosphoenolpyruvate (PEP) carboxylase, and it has no oxygenase activity and has a much higher affinity for CO2 than rubisco.

What is the reaction that Rubisco catalyzes?

Rubisco catalyses the primary photosynthetic CO2 reduction reaction, the fixation of atmospheric CO2 to ribulose-1,5-bisphosphate (RuBP) to form two molecules of 3-phosphoglycerate (3PGA), which is subsequently used to build the organic molecules of life.

What is Rubisco and PEP?

Some plants are able to combat the limitations of Rubisco and the C3 pathway. They have another carbon fixing enzyme in addition to Rubisco; this is often phosphoenolpyruvate carboxylase (PEP carboxylase). This catalyses the conversion of 3 carbon phosphoenolpyruvate (PEP) to oxaloacetete, using hydrogencarbonate ions.

What is PEP carboxylase activated by?

The enzyme is activated in the light by the phosphorolytic cleavage of the threonine phosphate group. Thus, the regulation of pyruvate phosphate dikinase proceeds in a completely different way from the regulation of PEP carboxylase.

Where is PEP carboxylase found in the chloroplast?

mesophyll cells
PEP carboxylase, which is located in the mesophyll cells, is an essential enzyme in C4 plants. In hot and dry environments, carbon dioxide concentrations inside the leaf fall when the plant closes or partially closes its stomata to reduce water loss from the leaves.

Why is PEP carboxylase better than rubisco?

C4 plants have carboxylating enzymes that have a higher affinity for CO2, compared to rubisco, especially at low CO2 concentrations & high temperatures. The C4 pathway uses PEP carboxylase, which has a much higher affinity for CO2 than rubisco; in addition, PEP carboxylase does NOT have oxygenase activity.

How does the role of PEP carboxylase in C4 plants differ from the role of rubisco in C3 plants?

Explain the role of PEP carboxylase in C4 plants, including key differences between it and rubisco. This enzyme adds CO2 to phosphoenolpyruvate (PEP), forming the four-carbon product oxaloacetate. PEP carboxylase has a much higher affinity for CO2 than does rubisco and no affinity for O2.

Why is Rubisco and the reaction it catalyzes so important?

RuBisCO is important biologically because it catalyzes the primary chemical reaction by which inorganic carbon enters the biosphere. Phosphoenolpyruvate carboxylase, unlike RuBisCO, only temporarily fixes carbon.

Does PEP carboxylase bind to oxygen?

PEP-C can catalyze carbon fixation independently to light or oxygen, and even under very low CO2 concentrations in the tissues (contrary to Rubisco, that needs photosynthetic ATP to be activated and certain proportions of CO2 to O2); and besides, PEP-C is also able to recognize as a substrate HCO3, which is the …

Why does PEP carboxylase have low activity in dark leaves?

PEP carboxylase, the key enzyme of C 4 metabolism, is highly regulated. In darkened leaves, this enzyme has low activity because (1) the affinity of the enzyme to its substrate phosphoenolpyruvate is very low and (2) it is inhibited by low concentrations of malate.

What is the role of PEP carboxylase in the C4 cycle?

To prevent this wasteful process, plants increase the local CO 2 concentration in a process called the C 4 cycle. PEP carboxylase plays the key role of binding CO 2 in the form of bicarbonate with PEP to create oxaloacetate in the mesophyll tissue.

What is the function of phosphoenolpyruvate carboxylase?

Phosphoenolpyruvate carboxylase (also known as PEP carboxylase, PEPCase, or PEPC; EC 4.1.1.31, PDB ID: 3ZGE) is an enzyme in the family of carboxy-lyases found in plants and some bacteria that catalyzes the addition of bicarbonate (HCO3−) to phosphoenolpyruvate (PEP) to form the four-carbon compound oxaloacetate and inorganic phosphate:

What are the allosteric activators of PEP carboxylase?

The main allosteric activators of PEP carboxylase are acetyl-CoA and fructose-1,6-bisphosphate (F-1,6-BP). Both molecules are indicators of increased glycolysis levels, and thus positive feed-forward effectors of PEP carboxylase.