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Phosphoenolpyruvate (2-phosphoenolpyruvate, PEP) is the carboxylic acid derived from the enol of pyruvate and phosphate. It exists as an anion. PEP is an important intermediate in biochemistry. It has the highest-energy phosphate bond found (−61.9 kJ/mol) in organisms, and is involved in glycolysis and gluconeogenesis.
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 (HCO 3 −) to phosphoenolpyruvate (PEP) to form the four-carbon compound oxaloacetate and inorganic phosphate: [1]
Pyruvate, the conjugate base, CH 3 COCOO −, is an intermediate in several metabolic pathways throughout the cell. Pyruvic acid can be made from glucose through glycolysis , converted back to carbohydrates (such as glucose) via gluconeogenesis , or converted to fatty acids through a reaction with acetyl-CoA . [ 3 ]
PPDK converts pyruvate to PEP, which reacts with CO 2 to produce oxaloacetate. When CO 2 is released in the bundle sheath cells, pyruvate is regenerated, and the cycle continues. [8] Though the reaction catalysed by PPDK is reversible, PEP is favoured as the product in biological conditions.
Pyruvate kinase is the enzyme involved in the last step of glycolysis.It catalyzes the transfer of a phosphate group from phosphoenolpyruvate (PEP) to adenosine diphosphate (ADP), yielding one molecule of pyruvate and one molecule of ATP. [1]
When pyruvate kinase – the enzyme that normally catalyzes the reaction that converts PEP to pyruvate – is knocked out in mutants of Bacillus subtilis, PEPCK participates in one of the replacement anaplerotic reactions, working in the reverse direction of its normal function, converting PEP to OAA. [13]
PEP (phosphoenol pyruvate) group translocation, also known as the phosphotransferase system or PTS, is a distinct method used by bacteria for sugar uptake where the source of energy is from phosphoenolpyruvate (PEP). It is known to be a multicomponent system that always involves enzymes of the plasma membrane and those in the cytoplasm.
The resulting Pyruvate is transaminated to alanine, diffusing to the mesophyll. Alanine is finally transaminated to pyruvate (PYR) which can be regenerated to PEP by PPDK in the mesophyll chloroplasts. This cycle bypasses the reaction of malate dehydrogenase in the mesophyll and therefore does not transfer reducing equivalents to the bundle sheath.