PPP@生物化学精品讲义

Rapidly dividing cells require more ribose 5- phosphate
than NADPH.
The need for NADPH and ribose 5-phosphate is balanced.
More NADPH is needed than ribose 5-phosphate; Fatty acid synthesis in adipose cells.
Regeneration of reduced glutathione requires NADPH produced in the Pentose Phosphate Pathway.
Glutathione Reductase catalyzes: GSSG + NADPH + H+ 2 GSH + NADP+
Transaldolase
transfers a three-carbon unit
+
5
5
+
3
7
+
6
4
+
4
5
C5 + C5 --来自百度文库 C7 + C3 C7 + C3 --> C4 + C6 C5 + C4 --> C6 + C3
+
6
3
Sum: 3C5 --> 2C6 + C3
Variations on the Pentose Phosphate Pathway
1) More ribose-5-P than NADPH is needed 2) Both ribose-5-P and NADPH are needed 3) More NADPH than ribose-5-P is needed 4) NADPH and ATP are needed, but ribose-5-P is not
The cell needs both NADPH and ATP
The use of NADPH
•Biosynthesis
• fatty acids • photosynthesis • DNA synthesis
•Redox regulation of cellular processes
• control of cellular redox state • transcription • disulfide bond formation • antioxidant defense
Pentose Phosphate Pathway
Aka: Pentose shunt Hexose monophosphate shunt Phosphogluconate pathway ☻It occurs in the cytosol.
☻Two oxidative processes followed by five nonoxidative steps ☻Operates active in the cytosol of liver and adipose cells
Regulatory enzyme
The enzyme is highly specific for NADP+; the Km for NAD+ is 1000 greater than for NADP+.
The Nonoxidative Phase
Transketolase
transfer of two-carbon units
Pentose Phosphate Pathway
• Cells need a constant supply of energy • NADH, NADPH and ATP • ATP - energy currency • NADPH - reducing power • Glucose --> NADH --> ATP • Glucose --> NADPH --> biosynthesis (reductive)
2 GSH + ROOH GSSG + ROH + H2O
Glutathione Peroxidase uses the trace element selenium as functional group. The enzyme's primary structure includes an analog of cysteine, selenocysteine, with Se replacing S.
• Irreversible 1st step - highly regulated (inhibited by NADPH)
• Gluconolactonase
• Uncatalyzed reaction happens too
• 6-Phosphogluconate Dehydrogenase
• An oxidative decarboxylation
Genetic deficiency of Glucose-6-P Dehydrogenase can lead to hemolytic anemia, due to inadequate [NADPH] within red blood cells.
Pentose Phosphate Pathway
• Provides NADPH • Produces ribose-5-P
Glycogen
Glucose
30%
Glucose-6-P
PPP
70%
Fructose-6-P
Glycolysis
Oxidative Phase
• Glucose-6-P Dehydrogenase
Glutathione and NADPH
☻What is glutathione? ☻Why is it important? ☻How is it related to NADPH?
Glutathione Peroxidase catalyzes degradation of organic hydroperoxides by reduction, as two glutathione molecules (represented as GSH) are oxidized to a disulfide.