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Phosphoenolpyruvate carboxylase

 

 
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Phosphoenolpyruvate carboxylase
 
 
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Phosphoenolpyruvate carboxylase (also known as PEP carboxylase, PEPCase, or PEPC; ) is an enzyme
Enzyme

Enzymes are biomolecules that catalysis chemical reactions. Almost all enzymes are proteins. In enzymatic reactions, the molecules at the beginning of the process are called Substrate , and the enzyme converts them into different molecules, the products....
 in the family of carboxy-lyases
Carboxy-lyases

Carboxy-lyases, also known as decarboxylases, are carbon-carbon lyases lyases that add or remove a carboxyl group from organic compounds....
 that catalyzes the addition of CO2
Carbon dioxide

Carbon dioxide is a chemical compound composed of two oxygen atoms covalent bond to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state....
 to phosphoenolpyruvate
Phosphoenolpyruvate

Phosphoenolpyruvic acid , or phosphoenolpyruvate as the anion, is an important chemical compound in biochemistry. It has the high-energy phosphate bond found in living organisms, and is involved in glycolysis and gluconeogenesis....
 (PEP) to form the four-carbon compound oxaloacetate:

PEP + CO2 ? oxaloacetate + Pi


This reaction is used for carbon fixation
Carbon fixation

Carbon fixation is a process found in autotrophs , usually driven by photosynthesis, whereby carbon dioxide is changed into organic materials. Carbon fixation can also be carried out by the process of calcification in marine, calcifying organisms such as Emiliania huxleyi....
 in so-called "CAM"
Crassulacean acid metabolism

Crassulacean acid metabolism, also known as CAM photosynthesis, is an elaborate carbon fixation pathway in some plants. These plants fix carbon dioxide during the night, storing it as the four carbon acid malate....
 and "C4" plants
C4 carbon fixation

C4 carbon fixation is one of three biochemical mechanisms, along with C3 carbon fixation and CAM photosynthesis, functioning in land plants to "fix" carbon dioxide for sugar production through photosynthesis....
 where it plays a key role in photosynthesis
Photosynthesis

File:Seawifs global biosphere.jpgPhotosynthesis is a metabolic pathway that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight....
.






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Phosphoenolpyruvate carboxylase (also known as PEP carboxylase, PEPCase, or PEPC; ) is an enzyme
Enzyme

Enzymes are biomolecules that catalysis chemical reactions. Almost all enzymes are proteins. In enzymatic reactions, the molecules at the beginning of the process are called Substrate , and the enzyme converts them into different molecules, the products....
 in the family of carboxy-lyases
Carboxy-lyases

Carboxy-lyases, also known as decarboxylases, are carbon-carbon lyases lyases that add or remove a carboxyl group from organic compounds....
 that catalyzes the addition of CO2
Carbon dioxide

Carbon dioxide is a chemical compound composed of two oxygen atoms covalent bond to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state....
 to phosphoenolpyruvate
Phosphoenolpyruvate

Phosphoenolpyruvic acid , or phosphoenolpyruvate as the anion, is an important chemical compound in biochemistry. It has the high-energy phosphate bond found in living organisms, and is involved in glycolysis and gluconeogenesis....
 (PEP) to form the four-carbon compound oxaloacetate:

PEP + CO2 ? oxaloacetate + Pi


This reaction is used for carbon fixation
Carbon fixation

Carbon fixation is a process found in autotrophs , usually driven by photosynthesis, whereby carbon dioxide is changed into organic materials. Carbon fixation can also be carried out by the process of calcification in marine, calcifying organisms such as Emiliania huxleyi....
 in so-called "CAM"
Crassulacean acid metabolism

Crassulacean acid metabolism, also known as CAM photosynthesis, is an elaborate carbon fixation pathway in some plants. These plants fix carbon dioxide during the night, storing it as the four carbon acid malate....
 and "C4" plants
C4 carbon fixation

C4 carbon fixation is one of three biochemical mechanisms, along with C3 carbon fixation and CAM photosynthesis, functioning in land plants to "fix" carbon dioxide for sugar production through photosynthesis....
 where it plays a key role in photosynthesis
Photosynthesis

File:Seawifs global biosphere.jpgPhotosynthesis is a metabolic pathway that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight....
. The enzyme is also found in some bacteria, but not in animals or fungi.

PEP carboxylase in photosynthesis

Carbon fixation via PEP carboxylase assimilates the available CO2 into a four-carbon compound (oxaloacetate, which is further converted to malate) that can be stored or shuttled between plant cells. This allows for a separation of initial CO2 fixation by contact with air and secondary CO2 fixation into sugars by RuBisCO
RuBisCO

Ribulose-1,5-bisphosphate carboxylase/oxygenase, most commonly known by the shorter name RuBisCO, is an enzyme that is used in the Calvin cycle to catalyze the first major step of carbon fixation, a process by which the atoms of atmospheric carbon dioxide are made available to organisms in the form of fuel molecules such as sucrose....
 during the light-independent reaction
Light-independent reaction

Photosynthesis, the light-independent reactions, are chemical reactions that convert carbon dioxide and other Chemical compounds into glucose. They occur in the stroma, the fluid filled area of a chloroplast outside of the thylakoid membranes....
s of photosynthesis.

In succulent CAM plants adapted for growth in very dry conditions, PEP carboxylase fixes CO2 during the night when the plant opens its stomata
Stoma

In botany, a stoma is a pore, found in the leaf and stem epidermis that is used forgas exchange. The pore is formed by a pair of specialized parenchyma cells known as guard cells which are responsible for regulating the size of the opening....
 to allow for gas exchange. During the day time, the plant closes the stomata to preserve water and releases CO2 inside the leaf from the storage compounds produced during the night. This allows the plants to thrive in dry climates by conducting photosynthesis without losing water through open stomata during the day.

In C4 plants, for example maize, PEP carboxylase fixes CO2 in the mesophyll cells of the leaf and the resulting four-carbon compound, malate, is shuttled into the bundle sheath cells where it releases CO2 for fixation by RuBisCO. Thus, the two processes are separated spatially, allowing for RuBisCO to operate in a low-oxygen environment to circumvent photorespiration
Photorespiration

Photorespiration is the alternate pathway for production of glyceraldehyde 3-phosphate by RuBisCO, the main enzyme of the light-independent reactions of photosynthesis ....
. Photorespiration occurs due to the inherent oxygenase
Oxygenase

An oxygenase is any enzyme that redox a Substrate by transferring the oxygen from molecular oxygen O2 to it. The oxygenases form a class of oxidoreductases; their EC number is EC 1.13 or EC 1.14....
 activity of RuBisCO in which the enzyme uses oxygen instead of carbon dioxide without incorporating carbon into sugars or generating ATP
Adenosine triphosphate

This article is about the chemical used by cells as an energy carrier. For other uses, see ATP .Adenosine-5'-triphosphate is a multifunctional nucleotide, and plays an important role in cell biology as a coenzyme that is the "molecule unit of currency" of intracellular energy transfer....
. As such, it is a wasteful reaction for the plant. By comparison, C4 carbon fixation via PEP carboxylase is more efficient.

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