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Chapter 17

BCM 475 Chapter Notes - Chapter 17: Thiamine Pyrophosphate, Acetyl-Coa, Lipoamide


Department
Biochemistry
Course Code
BCM 475
Professor
Welch
Chapter
17

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PYRUVATE DEHYDROGENASE COMPLEX (PDH COMPLEX)
IRREVERSIBLE LINK GLYCOLYSIS-CAC
Aerobic conditions: pyruvate transported into mitochondria for Oxidative Decarboxylation
Pyruvate + CoA + NAD+ acetyl CoA + CO2 + NADH + H+
STRUCTURE
- Large, integrated complex of 3 enzymes and 5 coenzymes
o Allow easy transfer of groups between active sites
(use of tethers)
AEROBIC CONDITIONS ONLY
- Glycolysis both aerobic/anaerobic | CAC only aerobic
- NAD and FAD+ can be regenerated only by the transfer of e-
to oxygen
SUBSTRATE CHANNELING
- Reaction product can pass directly amongst active sites by
connected channels
- Close arrangement of enzymes enhances CAC efficiency
- Described as metabolon
ATP or GTP: Bacteria use either ATP or GTP
NET RESULTS:
1 acetyl unit generates ~10ATP molecules
- 1 ATP generated in one CAC
- 9 ATP generated from the oxidation by the ETC of 3 NADH and 1 FADH2
- Net Stoichiometry:
o 2.5 ATP per 1NADH
o 1.5 ATP per 1 FADH2
CONVERSION OF PYRUVATE ACETYL CoA
3 Steps: coupled to preserve the free energy derived from decarboxylation
. DECARBOXYLATION
Pyruvate + TPP --> Hydroxyethyl-TPP + CO2
Catalyzed by: Pyruvate Dehydrogenase Component (E1)
Prosthetic Group: thiamine pyrophosphate (TPP)
. OXIDATION
Hydroxyethyl-TPP + Lipoamide TPP carbanion + Acetyl lipoamide
Catalyzed by: Pyruvate Dehydrogenase Component (E1)
5 Coenzymes
Catalytic
1. Thiamine pyrophosphate
(TPP)
2. Lipoic acid (derived as
lipoamide)
3. FAD
Stoichiometric/Substrates
4. CoA
5. NAD+
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