Pentose Phosphate Pathway (PPP) PDF

Pentose Phosphate Pathway (PPP) Glucose is catabolised by way of glycolytic pathway in to two molecules of pyruvate , then pyruvate is oxidized by citric acid cycle to produce ATP In animal tissue. There is an another metabolic pathway, called as the Pentose Phosphate Pathway (PPP), which is also...

Pentose Phosphate Pathway (PPP) Glucose is catabolised by way of glycolytic pathway in to two molecules of pyruvate , then pyruvate is oxidized by citric acid cycle to produce ATP In animal tissue. There is an another metabolic pathway, called as the Pentose Phosphate Pathway (PPP), which is also termed as Hexose Monophosphate Pathway (HMP shunt) -or Phosphogluconate pathway. this pathway generate Ribose sugar, ATP, two NADPH. Pentose Phosphate Pathway, is a metabolic pathway parallel to glycolysis. is special because no energy in the form of ATP is produced or used up in this pathway. Site in the body: liver, adipose tissue, lactating mammary gland, cortex of adrenal gland. Site in the cell : Occurs in the cytosol of the Cells. Function of pathway  The generation of reducing equivalents, in the form of NADPH, used in reductive biosynthesis reactions within cells (e.g. fatty acid synthesis).  Production of ribose 5-phosphate (R5P), used in the synthesis of nucleotides and nucleic acids.  Production of erythrose 4-phosphate (E4P) used in the synthesis of aromatic amino acids. The PPP can be divided into following phases 1.The oxidative (non- reversible) phase 2.The non oxidative (reversible) phase First phase: oxidative- non, reversible phase. In this phase, glucose 6- phosphate undergoes dehydrogenation and decarboxylation to yield a pentose, ribulose 5- phosphate. Second phase: a non-oxidative, reversible phase. In this phase, ribulose 5-phosphate is converted back to glucose 6-phosphate by a series of reactions involving mainly two enzymes: transketolase and transaldolase.  There are two distinct phases in the pathway. The first is the oxidative phase, in which NADPH is generated, and the second is the non-oxidative synthesis of 5-carbon sugars. For most organisms  oxidative phase 1- Enzyme: Glucose -6-phosphate dehydrogenase The first reaction of the pentose phosphate pathway is the oxidation of glucose 6-phosphate by glucose 6-phosphate dehydrogenase (G6PD) to form 6- phosphoglucono-lactone,and formation NADPH. 2- Enzyme: Lactonase The lactone is hydrolyzed to the free acid 6-phosphogluconate by a specific lactonase. 3- Enzyme: 6-Phospho gluconate dehydrogenase 6-phosphogluconate undergoes oxidation and decarboxylation by 6- phosphogluconate dehydrogenase to form the D ribulose 5-phosphate.so as NADPH.  4- Enzyme: Phosphopentose isomarase D ribulose 5-phosphate convert to D ribose 5- phosphopentose by isomerase. it’s the only reaction is reversible in phospho pentos bathway. NON OXIDATIVE PHASE Conversion of pentose phosphate to glucose -6 phosphate  In cell that require high level of NADPH for biosynthetic reaction, the ribulose -5P produced in the oxidative phase need to be a turn back in to a glucose -6 phosphate to maintain flux through the glucose -6P dehydrogenase reaction  The carbon shuffle reaction of non-oxidative phase which ultimately are used to regenerate glucose -6P using transketolase and trans aldolase enzyme. 5- Enzyme: Ribulose -5 phosphate epimerase 6- Enzyme: Trans ketolase and trans aldolase This step isessential to change pentose back to glucose ,but beside to epimarase, two enzymes namely (i) Trans ketolase and (ii) Transaldolase are needed. Note: Transketolase requires the cofactor thiamine pyrophosphate (TPP)