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PENTOSE PHOSPHATE PATHWAY, LATO, Enzyme, Substrate, Product, Rate limiting…
PENTOSE PHOSPHATE PATHWAY
Phases
Oxidative / Irreversible
Products
2 NADPH
1 Ribulose 5 Phosphate
1 CO2
Hydrolysis
6 Phosphogluconolactone
Gluconolactonase
6 Phosphogluconate
Oxidation / Decarboxylation
6 Phosphogluconate
6 Phosphogluconate dehydrogenase
Ribulose 5 Phosphate, NADPH, CO2
Oxidation
Glucose 6 Phosphate
G6P Dehydrogenase
6 Phosphogluconolactone, NADPH
Non-oxidative / Reversible
Products
2 Fructose 6 Phosphate
1 Glyceraldehyde 3 Phosphate
1 Ribose 5 Phosphate
Intermediate of glycolysis
Shuttled back to glycolysis
Conversion of ribulose 5 phosphate to ribose 5 phosphate & xylulose 5 phosphate
Isomerization
Ribulose 4 Phosphate
Epimerase
Xylulose 5 Phosphate
Transfer of C atoms
Ribose 5 Phosphate, Xylulose 5 Phosphate
Transketolase
Glyceraldehyde 3 Phosphate, Sedoheptulose 7 Phosphate
Transfer of C atoms
Sedoheptulose 7 Phosphate
Transaldolase
Erythrose 4 Phosphate, Fructose 6 Phosphate
Transfer of glycoaldehyde group
Erythrose 4 Phosphate
Transketolase
Glyceraldehyde 3 Phosphate, Fructose 6 Phosphate
Isomerization
Ribulose 5 Phosphate
Isomerase
Ribose 5 Phosphate
Functions
Forms NADPH for fatty acid/ steroid synthesis
Produce ribose precursor for nucleotide and nucleic acid formation
Maintain reduced glutathione
Sites
Fatty acid synthesis
Adipose
Lactating Mammary gland
Liver
Cholesterol/Steroid synthesis
Adrenal
Testes
Liver
Ovary
Shunt / Alternate Pathway
Produces NADPH & CO2, not ATP
Biomedical Importance
Prolongs RBC lifespan
NADPH removes H2O2 = prevents oxidative damage
G6PD Deficiency
Causes hemolytic anemia
NADPH synthesis deficiency = RBC membrane damage
Regulation of PPP
Cell NEEDS MORE NADPH
Ribose-5-P converted to Fructose-6-P & Glyceraldehyde-3-P
Enters glycolytic pathway
Cells NEEDS TO SYNTHESIZE nucleotides
Fructose-6-P & Glyceraldehyde 4-P converted to Ribose 5-P
Reversal of transketolase & transaldolase reaction
LATO
Enzyme
Substrate
Product
Rate limiting step
Reaction
Reaction
Substrate
Product
Enzyme