[PSM] Pentose Phosphate Pathway

G6P Dehydrogenase

Enzyme: G6P → 6-Phosphogluconolactone

G6P → 6-Phosphogluconolactone (Oxidative Step 1)

Reaction: G6P Dehydrogenase

Lactonase

Enzyme: 6-Phosphogluconolactone → 6-Phosphogluconate

6-Phosphogluconolactone → 6-Phosphogluconate (Oxidative Step 2)

Reaction: Lactonase

6-Phosphogluconate dehydrogenase

Enzyme: 6-Phosphogluconate → Ribulose-5-Phosphate + CO2

6-Phosphogluconate → Ribulose-5-Phosphate + CO2 (Oxidative Step 3)

Enzyme: 6-Phosphogluconate dehydrogenase

Ribose-5-phosphate isomerase

Enzyme: Ribulose-5-phosphate → Ribose-5-phosphate

Ribulose-5-phosphate → Ribose-5-phosphate (Non-Oxidative Step 1)

Reaction: Ribose-5-phosphate isomerase

Ribulose-5-phosphate → Xylulose-5-phosphate (Non-Oxidative Step 2)

Reaction: Epimerase

Epimerase

Enzyme: Ribulose-5-phosphate → Xylulose-5-phosphate

Ribose-5-P + Xylulose-5-P → G3P + Sedoheptulose-7-P (Non-Oxidative Step 3)

Reaction: Transketolase

Transketolase

Ribose-5-P + Xylulose-5-P → G3P + Sedoheptulose-7-P (Non-Oxidative Step 3)

G3P + Sedoheptulose-7-P → F6P + Erythrose-4-P (Non-Oxidative Step 4)

Reaction: Transaldolase

Transaldolase

Enzyme: G3P + Sedoheptulose-7-P → F6P + Erythrose-4-P (Non-Oxidative Step 4)

NADPH (can reduce glutathione to GSH to neutralize ROS)
Ribose-5-Phosphate (nucleotide synthesis) - from oxidative
G3P + F6P (can re-enter glycolysis) - from nonoxidative

What are the key outputs of the PPP

G6P → 6-phosphogluconolactone + NADPH (via G6P dehydrogenase)

Rate limiting step of the PPP

Cytoplasm

Where does PPP occur in the cell?

NADP+ availability (positive regulator)

What regulates G6PD activity?

Oxidative - irreversible
Nonoxidative - reversible

Which among the oxidative and nonoxidative phases are reversible?