★ Master Switch of Glycolysis — available now
PFKFB3 (iPFK-2 / FBPase-2)
F6P + ATP → F2,6BP + ADP + H⁺ | F2,6BP + H₂O → F6P + Pᵢ
Bifunctional kinase + phosphatase that sets the level of F2,6BP, the most potent allosteric activator of PFK-1. Two active sites, two separate mechanisms.
EC 2.7.1.105 / EC 3.1.3.46 · PDB 2AXN·2DWP·2I1V·3QPV·3QPW
▶ OPEN SIMULATORWhy it matters: PFKFB3 controls glycolytic flux by making and breaking fructose-2,6-bisphosphate. Overexpressed in cancer cells (Warburg effect); a major drug target.
The 10 Glycolytic Steps
Hexokinase I HK1 · not glucokinase (GCK)
Glucose + ATP → G6P + ADP
Induced-fit domain closure toward glucose (drawn — bound alone, glucose doesn't seal the C-terminal cleft); Mg²⁺-assisted in-line phosphoryl transfer; conserved Asp657 proposed as catalytic base.
EC 2.7.1.1 · human HK1
▶ OPEN SIMULATORPhosphoglucose isomerase (PGI)
G6P ⇌ F6P
Aldose-ketose isomerization: ring opening, base-catalyzed proton abstraction via cis-enediol(ate) intermediate, ring closure.
EC 5.3.1.9
▶ OPEN SIMULATORPhosphofructokinase-1 (PFK-1)
F6P + ATP → F1,6BP + ADP
Rate-limiting committed step. Allosterically activated by AMP & F2,6BP, inhibited by ATP/citrate. In-line phosphoryl transfer onto the 1-OH.
EC 2.7.1.11
▶ OPEN SIMULATORAldolase (class I)
F1,6BP ⇌ DHAP + G3P
Retro-aldol cleavage through a Schiff-base (protonated imine) between Lys and C2 of the sugar; stabilized carbanion intermediate.
EC 4.1.2.13
▶ OPEN SIMULATORTriosephosphate isomerase (TPI)
DHAP ⇌ G3P
The perfect enzyme: kcat/KM near the diffusion limit in GAP→DHAP. Glu165 abstracts the pro-R proton from the CH₂OH end of DHAP to a cis-enediolate stabilized by His95/Lys12, then reprotonates C2 to give D-G3P; the loop-6 "lid" seals the pocket.
EC 5.3.1.1
▶ OPEN SIMULATORGAPDH (oxidation → acyl phosphate)
G3P + Pᵢ + NAD⁺ → 1,3-BPG + NADH
Cys152 thiolate attacks the aldehyde → thiohemiacetal; hydride transfer to NAD⁺; phosphorolysis of the thioester → acyl phosphate.
EC 1.2.1.12
▶ OPEN SIMULATORPhosphoglycerate kinase (PGK)
1,3-BPG + ADP → 3PG + ATP
First ATP-producing step (substrate-level phosphorylation). Two domains hinge closed (arc ≈32° [schematic]; frame 2XE7 is semi-closed); the TS is neutralized by a basic patch (Arg38 · Lys215 · Lys219) and Mg²⁺, while Arg122/Arg65/Arg170 + His62 clamp the 3-phosphate.
EC 2.7.2.3
▶ OPEN SIMULATORPhosphoglycerate mutase (dimeric PGAM)
3PG ⇌ 2PG
Phosphohistidine (His11) shuttle: enzyme phosphorylates the substrate, then reclaims the phosphate at the adjacent position — a Ping-Pong swap.
EC 5.4.2.11
▶ OPEN SIMULATOR