Biochemistry: A Short Course

1
Glycolysis and Citric Acid Cycle Bridged via
Pyruvate Dehydrogenase
2
Glycolysis are Cytosolic Enzymes While
Mitochondria Complete Respiration
Pyruvate is moved from the cytosol to the
mitochondrion Matrix membrane permeability is
critical
3
Citric Acid Entry Point Acetyl CoA
4
Pyruvate Dehydrogenase Complex
5
Pyruvate Dehydrogenase Complex
Complex 4-10 million daltons with 3 distinct
enzymes
6
Acetyl Coenzyme- A Formation from Pyruvate Three
Distinct Reactions
Irreversible reaction coupling glycolysis and
citric acid cycle Enzyme complex couples the
reaction steps together
What is the first reaction that looks iffy?
7
Electron Sink Needed
Thiamine pyrophosphate (TPP) pulls in electrons
8
Step 1 E1 (PDH) Decarboxylates Pyruvate
9
Step 2 E2 Oxidizes Hydroxyethyl- to
Acetyl-Dihydrolipoamide-E2
What is the structure of lipoic acid? What
reaction couples lipoic acid and lysine?
10
Step 3 E2 Oxidizes Hydroxyethyl- to Acetyl-and
Transfers Acetyl- to CoA
11
Step 4-5 E3 Oxidizes Reduced Dihydrolipoamide
and Reduces NAD
Proteins tightly associated with FAD
Flavoproteins
12
Pyruvate Dehydrogenase a Multi-Enzyme Complex
with 5 Cofactors CoA, NAD, Lipoamide, TPP
and FAD
13
Mechanism of Pyruvate ? Acetyl CoA
14
Transacetylase Core Structure (Red Balls)
Each red ball represents 3 E2 subunits Each
subunit contains three domains Transacetylase
domain has three subunits (1 shown in red)
15
Reaction Sites for Pyruvate Dehydrogenase
Catalysis
16
Reaction Sites for Pyruvate Dehydrogenase
Catalysis
Intermediate Order? Dihydrolipoamide, Acetyl
CoA, Coenzyme A, FADH2, Acetylipoamide,
Lipoamide, Pyruvate, Hydroxyethyl-TPP, and NADH
17
Reaction Sites for Pyruvate Dehydrogenase
Catalysis
Intermediate Order? Dihydrolipoamide, Acetyl
CoA, Coenzyme A, FADH2, Acetylipoamide,
Lipoamide, Pyruvate, Hydroxyethyl-TPP, and NADH
18
Pyruvate Dehydrogenase Component (E1) Deactivated
via Phosphorylation
19
High Energy Charge Down Regulates Pyruvate
Dehydrogenase
20
Arsenite Poisoning via Pyruvate Dehydrogenase
Inhibition
What step is inhibited by arsenite?
21
Test Your Understanding
Would you expect that thiamine thiazolone
pyrophosphate is a potential pyruvate
dehydrogenase competitive inhibitor for TPP?
22
Chapter 18 Problems 1-10