5P Regulation

Pentose Phosphate Pathway

Pentose Phosphate Pathway Regulation

Fundamentals

• NADP concentration (inverse positive? inhibition)
  • DEC NADP conc = DEC enzymatic activity of the nonoxidative interconversions
    • WHY? fewer oxidzing agents
• NADPH concetration (competitive inhibition)
  • Intensifies the NADP effects
    • HOW? competiting for active sites further DEC enzymatic activity

Rate Limiting Step

• Dehydrogenation of Glucose 6-phosphate
  • WHY? Irreversible

Control Site

• Dehydrogenation of Glucose 6-phosphate
  • WHY? Irreversible
• Need for NADPH, Ribose 5-phosphate and ATP regulates 5P Pathway
  • Alters the different in 4 metabolic situations:

Detailed Regualtion of Glucose 6-Phosphate

Glycolytic - Indirect Pentose Phosphate

• Mode 1: Ro5P>NADPH - Nonxidative Phase Favored
• 1)G6P --> DHAP --> GAP ===> Ribose 5-phosphate
• 2)G6P --> Fructose 6-phosphate ===> Ribose 5-phosphate
  • Rapidly dividng cells - Mitosis/Meiosis
    • 5XGlucose 6-phosphate + ATP -> 6XRibose 5-phosphate + ADP + H

Glycolytic - Direct Pentose Phosphate

• Mode 2: Ro5P=NADPH - Oxidative Phase Favored
• G6P --> Ribulose 5-phosphate ===> Ribose 5-phosphate
  • DNA replication w/ Fatty acid synthesis - Liver
    • Glucose 6-phosphate + 2NADP + H2O --> Ribose 5-phosphate + 2NADPH + H + CO2

Pentose Phosphate-Gluconeogenic Cycle

• Mode 3: Ro5P<nadph - Nonoxidative and Oxidative Phases Favored
  • Steroid Synthesis - Endocrine System
    • Glucose 6-phospahte + 12 NADP + 7H2O --> 6CO2 + 12NADPH + 12H + Pi

Glycolitic - Direct Pentose Phosphate --> Glycolitic-Pentose Phosphate

• Mode 4: NADPH=ATP - Nonoxidative and Oxidative Phases Favored
  • DNA replication w/ Fatty acid synthesis
    • 3XGlucose 6-phosphate + 6NADP + 5NAD + 5Pi + 8ADP --> 5XPyruvate + 3CO2 + 6NADPH + 5NADH + 8ATP + 2H2O + 8H

Concepts:

• Rate Limiting Step: CHEM
• Oxidation
• Inhibition