Pentose phosphate pathway — oxidative NADPH + non-oxidative sugar shuffle
Branches from G6P. The oxidative arm (G6PD · PGLS · PGD) yields NADPH and ribulose 5-phosphate. The non-oxidative arm (RPI / RPE · TKT · TALDO) feeds R5P to nucleotides and returns F6P + GAP to glycolysis. No net H⁺ on the non-oxidative pages.
Glucose-6-phosphate dehydrogenase G6PD
G6P + NADP⁺ → 6PGL + NADPH + H⁺
Committed oxidative step. His263 abstracts the C1-OH proton; hydride to NADP C4. Immediate product is the δ-lactone, not 6-phosphogluconate. Structural NADP is a second occupant.
EC 1.1.1.49 · PDB 2BH9
▶ OPEN SIMULATOR6-Phosphogluconolactonase PGLS
6PGL + H₂O → 6PG + H⁺
Lactone hydrolysis. Mesh is T. maritima 1PBT — human PGLS has no PDB. His138 activates water; OH⁻ opens C1. H6PD is a different gene.
EC 3.1.1.31 · PDB 1PBT
▶ OPEN SIMULATOR6-Phosphogluconate dehydrogenase PGD
6PG + NADP⁺ → Ru5P + CO₂ + NADPH + H⁺
Oxidative decarboxylation at a dimer interface. Lys184B / Glu191B come from the partner subunit. Second NADPH of oxidative PPP; Ru5P feeds RPI and RPE.
EC 1.1.1.44 · PDB 2JKV
▶ OPEN SIMULATORRibose-5-phosphate isomerase RPI
Ru5P ⇌ R5P
Aldose–ketose isomerization. Mesh is E. coli 1O8B — human RPIA has no PDB. R5P feeds nucleotides and TKT. Not RPE (that enzyme makes Xu5P).
EC 5.3.1.6 · PDB 1O8B
▶ OPEN SIMULATORRibulose-5-phosphate 3-epimerase RPE
Ru5P ⇌ Xu5P
C3 epimerization. Deposited Fe²⁺ is the Lewis acid; Asp37 / Asp175 invert C3. Xu5P is the ketol donor for TKT.
EC 5.1.3.1 · PDB 3OVP
▶ OPEN SIMULATORTransketolase TKT · TPP
Xu5P + R5P ⇌ S7P + GAP | Xu5P + E4P ⇌ F6P + GAP
One enzyme, two ketol shuffles, one crystal. TPP C2 ylide; sugars are schematic on 3MOS. TALDO uses S7P + GAP next.
EC 2.2.1.1 · PDB 3MOS
▶ OPEN SIMULATORTransaldolase TALDO1 · Schiff Lys142
S7P + GAP ⇌ E4P + F6P
Class-I aldolase. Lys142 Schiff on apo 1F05 — every sugar is schematic. F6P and GAP return to glycolysis. Not TKT (that enzyme uses TPP).
EC 2.2.1.2 · PDB 1F05
▶ OPEN SIMULATOR