1. Reginald Garrett and Charles Grisham
Chapter 19
Glycolysis
to accompany
Biochemistry, 2/e by
Reginald Garrett and Charles Grisham
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2. Outline 19.1 Overview of Glycolysis
19.2 Coupled Reactions in Glycolysis
19.3 First Phase of Glycolysis
19.4 Second Phase of Glycolysis
19.5 Metabolic Fates of NADH and Pyruvate
19.6 Anaerobic Pathways for Pyruvate
19.7 Energetic Elegance of Glycolysis
19.8 Other Substrates in Glycolysis

3. Overview of Glycolysis
The Embden-Meyerhof (Warburg) Pathway
Essentially all cells carry out glycolysis
Ten reactions - same in all cells - but rates differ
Two phases:
First phase converts glucose to two G-3-P
Second phase produces two pyruvates
Products are pyruvate, ATP and NADH
Three possible fates for pyruvate

5. First Phase of Glycolysis
The first reaction - phosphorylation of glucose
Hexokinase or glucokinase
This is a priming reaction - ATP is consumed here in order to get more later
ATP makes the phosphorylation of glucose spontaneous
Be SURE you can interconvert Keq and standard state free energy change
Be SURE you can use Eq to generate far right column of Table 19.1

9. Hexokinase 1st step in glycolysis; G large, negative
Hexokinase (and glucokinase) act to phosphorylate glucose and keep it in the cell
Km for glucose is 0.1 mM; cell has 4 mm glucose
So hexokinase is normally active!
Glucokinase (Kmglucose = 10 mM) only turns on when cell is rich in glucose
Hexokinase is regulated - allosterically inhibited by (product) glucose-6-P - but is not the most important site of regulation of glycolysis - Why?

12. Rx 2: Phosphoglucoisomerase
Glucose-6-P to Fructose-6-P
Why does this reaction occur??
next step (phosphorylation at C-1) would be tough for hemiacetal -OH, but easy for primary -OH
isomerization activates C-3 for cleavage in aldolase reaction
Ene-diol intermediate in this reaction
Be able to write a mechanism!

14. Rx 3: Phosphofructokinase
PFK is the committed step in glycolysis!
The second priming reaction of glycolysis
Committed step and large, neg delta G - means PFK is highly regulated
ATP inhibits, AMP reverses inhibition
Citrate is also an allosteric inhibitor
Fructose-2,6-bisphosphate is allosteric activator
PFK increases activity when energy status is low
PFK decreases activity when energy status is high

20. C6 cleaves to 2 C3s (DHAP, Gly-3-P)
Rx 4: Aldolase
C6 cleaves to 2 C3s (DHAP, Gly-3-P)
Animal aldolases are Class I aldolases
Class I aldolases form covalent Schiff base intermediate between substrate and active site lysine
Understand the evidence for Schiff base intermediate (box on page 622)

24. Rx 5: Triose Phosphate Isomerase
DHAP converted to Gly-3-P
An ene-diol mechanism (know it!)
Active site Glu acts as general base
Triose phosphate isomerase is a near-perfect enzyme - see Table 14.5

28. Glycolysis - Second Phase
Metabolic energy produces 4 ATP
Net ATP yield for glycolysis is two ATP
Second phase involves two very high energy phosphate intermediates .
1,3 BPG
Phosphoenolpyruvate

30. Rx 6: Gly-3-Dehydrogenase
Gly-3P is oxidized to 1,3-BPG
Energy yield from converting an aldehyde to a carboxylic acid is used to make 1,3-BPG and NADH
Mechanism is one we saw in Chapter 16 (see Figure 16.10!)
Mechanism involves covalent catalysis and a nicotinamide coenzyme - know it

33. Rx 7: Phosphoglycerate Kinase
ATP synthesis from a high-energy phosphate
This is referred to as "substrate-level phosphorylation"
2,3-BPG (for hemoglobin) is made by circumventing the PGK reaction

36. Rx 8: Phosphoglycerate Mutase
Phosphoryl group from C-3 to C-2
Rationale for this enzyme - repositions the phosphate to make PEP
Note the phospho-histidine intermediates!
Zelda Rose showed that a bit of 2,3-BPG is required to phosphorylate His

39. Rx 9: Enolase 2-P-Gly to PEP Overall G is 1.8 kJ/mol
How can such a reaction create a PEP?
"Energy content" of 2-PG and PEP are similar
Enolase just rearranges to a form from which more energy can be released in hydrolysis

41. PEP to Pyruvate makes ATP
Rx 10: Pyruvate Kinase
PEP to Pyruvate makes ATP
These two ATP (from one glucose) can be viewed as the "payoff" of glycolysis
Large, negative G - regulation!
Allosterically activated by AMP, F-1,6-bisP
Allosterically inhibited by ATP and acetyl-CoA
Understand the keto-enol equilibrium of Py

45. The Fate of NADH and Pyruvate Aerobic or anaerobic??
NADH is energy - two possible fates:
If O2 is available, NADH is re-oxidized in the electron transport pathway, making ATP in oxidative phosphorylation
In anaerobic conditions, NADH is re-oxidized by lactate dehydrogenase (LDH), providing additional NAD+ for more glycolysis

46. The Fate of NADH and Py Aerobic or anaerobic??
Pyruvate is also energy - two possible fates:
aerobic: citric acid cycle
anaerobic: LDH makes lactate

48. Energetics of Glycolysis
The elegant evidence of regulation!
See Figure 16.31
Standard state G values are scattered: + and -
G in cells is revealing:
Most values near zero
3 of 10 Rxns have large, negative  G
Large negative  G Rxns are sites of regulation!

50. Other Substrates for Glycolysis
Fructose, mannose and galactose
Fructose and mannose are routed into glycolysis by fairly conventional means. See Figure 18.32
Galactose is more interesting - the Leloir pathway "converts" galactose to glucose - sort of....
See Figure 16.33