Pentose Phosphate Pathway Flashcards
Other names of Pentose Phosphate Pathway
Hexose Monophosphate Pathway
Phosphoglyconate Pathway
Pentose Monophosphate Shunt
Pentose Phosphate Pathway
-Function
1) Provides biosynthetic reduction power by synthesizing NADPH
2) Catabolism/Synthesis of C5 (pentoses) carbohydrates
- nucleotide biosynthesis
3) Catabolism/Synthesis of C4 (tetroses) carbohydrates
4) linked to glycolysis
Pentose Phosphate Pathway is divided into?
1) Oxidative Phase
- synthesis of NADPH
2) Nonoxidative Phase
- interconversion of C4-7 carbohydrates
Location of Pentose Phosphate Pathway to provide NADPH?
1) Synthesis
- Adrenal Gland-Steroid Synthesis
- Testes- Steroid Synthesis
- Ovary- Steroid Synthesis
- Mammary gland-Fatty Acid Synthesis
- Liver- Fatty acid and Cholesterol Biosynthesis
- Adipose Tissue-Fatty acid synthesis
- Various tissues-neurotransmitter biosynthesis
- Almost all tissue- nucleotide biosynthesis
2) Detoxification
- Reduction of oxidized glutathione
- Cytochrome P450 monooxygenase
Oxidative Phase overview:
-produces/reduces?
Produces:
1 Ribulose 5-phosphate
Reduces
2 NADP+ and Glucose 6-Phosphate
Glucose 6-Phosphate Dehydrogenase
Glucose 6-Phosphate-> 6-Phosphoglucono-8-lactone
- Irreversible/regulated
- NADP+ reduced to NADPH
- Glucose 6-P oxidized
- dehydrogenation Ron
INHIBITED:
by low NADP+ concentration
Lactonase
6-Phosphoglucono-8-lactone->6-Phosphogluconate
-Hydrolysis-ring opening at ketone group
6-Phosphogluconate Dehydrogenase
6-Phosphogluconate-> ribulose 5-Phosphate + CO2
- NADP+ reduced to NADPH
- loses Carbon 6C to 5C
Phosphopentose Isomerase
Ribulose 5-Phosphate-> Ribose 5-Phosphate
Phosphopentose Epimerase
Ribulose 5-Phosphate-> Xylulose 5-Phosphate
1st Step of Nonoxidative Phase
Xylulose 5-P + Ribose 5-P-> G3P + Sedheptulose 7-P
-Transketolase andTPP as coenzyme
2nd Step of Nonoxidative Phase
G3P + Sedheptulose -> Fructose 6-P + Erythrose 4-P
- Transaldolase
- uses R group of Lysine to form Schiff Base (no prosthetic group)
3rd Step of Nonoxidative Phase
Xylulose 5-P + Erythrose 4-P-> Fructose 6-P + G3P
-Transketolase
Similiarities in Transketolase and Transaldolase mechanisms:
Both enzymes produce carbanions stabilized by resonance during catalysis
1) transketolase-> TPP
2) transaldolase-> Lysine
Why does the Pentose Phosphate Pathway adjusts to Needs of the cell?
For production of NADPH or various carbohydrates
Situation 1:
High demand for ribose 5-Phosphate (for DNA synthesis; Low demand for NADPH
Does not Use oxidative phase only non oxidative:
Glycolysis is linked to Transketolase and transaldolase
Run it through the first few steps of Glycolysis
1) Glucose 6-P -> Fructose 6-P-> Fructose 1,6-BP-> DHAP +G3P
- 2 molecules of Fructose 6-P and 1 molecule of G3P produces 3 Molecules of ribose 5-Phosphate
Situation 2:
Balanced need for ribose 5-Phosphate and NADPH
Uses oxidative phase to produce 2 NADPH and 1 ribose 5-Phosphate
Situation 3:
More NADPH than ribose 5-Phosphate required
Glucose 6-P completely oxidized to CO2
3 reactions
-oxidative phase of Pentose Phosphate Pathway to produce ribulose 5-P
-Transketolase and Transaldolase to produce F 6-P and G3P
-Gluconeogenesis to convert Fructose 6-P and G3P back to Glucose 6-P
Situation 4:
Both NADPH and ATP required
1) Oxidative Phase of Pentose Phosphate Pathway
- Glucose 6-P-> Ribulose 5-Phosphate + CO2 + 2NADPH
2) Ribulose 5-P -> F6P and G3P via transketolase and transaldolase which enter glycolysis
3) Pyruvate is oxidized and used as precursors to produce ATP
Glutathione
- structure
- Protect?
- reaction?
Protects against Reactive Oxygen Species (ROS) when its in reduced form
Gluathione-tripeptide of ECG with a free sulfhydryl
**peptide bone to Glutamate is attached to R group
GSH-> GSSG
- GSH=reduced
- GSSH=oxidized
- catalyzed by Glutathione reductase containing FAD
- oxidized NADPH to NADP+
