Glycolysis Enzymes & Intermediates

Full Mnemonic

Hungry Peter Pan And The Growling Pink Panther Eat Pies (HPPATGPPEP)

H

Hexokinase - Glycolysis step 1 | glucose + ATP → G6P + ADP | kinase (phosphoryl group transfer) | traps glucose in the cell | irreversible | inhibited by G6P | bypassed in gluconeogenesis by glucose 6-phosphatase

P1

Phosphoglucose Isomerase - Glycolysis step 2 | G6P → F6P | isomerase (carbonyl moves from C1 to C2, aldose to ketose) | reversible, used in glycolysis AND gluconeogenesis | needed so C1 can be phosphorylated in step 3

P2

Phosphofructokinase-1 (PFK-1) - Glycolysis step 3 | F6P + ATP → F1,6BP + ADP | kinase | irreversible, main control point | activated by AMP and F2,6BP | inhibited by ATP and citrate | bypassed by fructose 1,6-bisphosphatase

A

Aldolase - Glycolysis step 4 | F1,6BP → DHAP + G3P | cleavage (retro-aldol) | carbanion stabilized by resonance with the carbonyl | splits 6C into two 3C

T

Triose Phosphate Isomerase - Glycolysis step 5 | DHAP ⇌ G3P | isomerase | only G3P continues, so consumption of G3P pulls the equilibrium | end of preparatory phase: 2 G3P per glucose

G

Glyceraldehyde 3-Phosphate Dehydrogenase - Glycolysis step 6 | G3P + Pi + NAD+ → 1,3-BPG + NADH + H+ | oxidation coupled to phosphorylation | the new phosphate comes from Pi (O atom is from Pi) | first NADH, 2 per glucose | first step of payoff phase

P3

Phosphoglycerate Kinase - Glycolysis step 7 | 1,3-BPG + ADP → 3PG + ATP | substrate-level phosphorylation | reversible | makes 2 ATP per glucose (pays back the 2 ATP invested)

P4

Phosphoglycerate Mutase - Glycolysis step 8 | 3PG → 2PG | mutase (isomerase that moves a phosphate within the same molecule) | sets up step 9

E

Enolase - Glycolysis step 9 | 2PG → PEP + H2O | dehydration (elimination of water, OH and H) | creates a high-energy enol phosphate (phosphate group stabilizes the enol form)

P5

Pyruvate Kinase - Glycolysis step 10 | PEP + ADP → pyruvate + ATP | substrate-level phosphorylation | irreversible (very negative ΔG) | activated by F1,6BP and AMP | inhibited by ATP, acetyl-CoA, alanine | bypassed by pyruvate carboxylase + PEPCK

Glycolysis Intermediates in Order

Glucose, G6P, F6P, F1,6BP, DHAP + G3P (2 G3P), 1,3-BPG, 3PG, 2PG, PEP, pyruvate

Net result of glycolysis (per glucose)

2 pyruvate + 2 NADH + 2 ATP net | preparatory phase (steps 1 to 5) spends 2 ATP | payoff phase (steps 6 to 10) makes 4 ATP | cytosol | ΔG'° values: steps 1, 3, 10 are the very negative (irreversible) ones

Which Steps Use ATP?

Steps 1 and 3 (hexokinase, PFK-1)

Which Steps Make ATP?

Steps 7 and 10 (phosphoglycerate kinase, pyruvate kinase)

Which Steps Make NADH?

Step 6 (GAPDH)