anaplerotic reactions
DESCRIPTION
Anaplerotic Reactions. CH339K. Citric Acid Cycle in Anabolism. Anaplerotic Reactions. ana : back; up; again; re- Plhrow : I fill Anaplerotic reactions refill the pools of Krebs cycle intermediates that would otherwise become depleted. Important Anaplerotic (Replenishing) Reactions. - PowerPoint PPT PresentationTRANSCRIPT
Anaplerotic Reactions
: back; up; again; re-
: I fill
Anaplerotic reactions refill the pools of Krebs cycle intermediates that would otherwise become depleted.
Pyruvate Carboxylase
• Mitochondrial enzyme• Two roles
• Gluconeogenesis• Anaplerosis
• 4 identical subunits• Biotin cofactor
PEP Carboxykinase
• Cytosolic enzyme active in gluconeogenesis• Mitochondrial enzyme active in anaplerosis
PEP Carboxylase
• Mechanism involves pyruvate enolate• Phosphate is transferred from PEP to bicarbonate• Pyruvate enolate then attacks the carboxyphosphate anhydride carbon• Sequesters carbon in some plants
Malic Enzyme
1) Reductive carboxylation2) Uses NADP+ as a cofactor instead of NAD+.3) Pyruvate carboxyl reduced to hydroxyl
Transaminations
• Every -amino acid has a conjugate -keto acid.
• Amino and keto conjugates are readily interconverted.
Gyoxylate Cycle
• Critters can make fat from carbohydrates • Plants, fungi, and some bacteria can make
carbohydrates from fats via acetyl-CoA• Use a modified version of the Krebs Cycle• Plants use this to grow from stored oils in
seeds• Bacteria use this to grow on simple carbon
compounds when carbohydrates are unavailable
• Critter exception – some nematodes in early stages can perform
The triffids that ate England were apparently quite dependent on the glyoxylate cycle to assimilate there quivering human prey…
The Glyoxylate Cycle
2 Acetyl-CoA + NAD+ + 2H2O -->succinate + 2CoA + NADH + H+
Compare with Citric Acid Cycle
Acetyl-CoA + 3NAD+ + FAD + GDP + Pi + 2H2O -->2CO2 + CoA + 3NADH + 3H+ + FADH2 + GTP