The pentose phosphate pathway has two phases: an oxidative phase that generates NADPH and a non-oxidative phase that synthesizes 5-carbon sugars. In the oxidative phase, glucose-6-phosphate is converted through several enzymatic reactions to produce two molecules of NADPH and one molecule of ribulose-5-phosphate. The non-oxidative phase involves isomerization and transketolase and transaldolase reactions that transfer carbon units to ultimately form fructose-6-phosphate and glyceraldehyde-3-phosphate from ribulose-5-phosphate. Overall, the pathway converts three molecules of glucose-6-phosphate to produce six molecules of NADPH, three molecules of carbon dioxide

1. Pentose phosphate
pathway

2. The pathway
There are two distinct phase in the
pathway
The first is the oxidative phase,in
which NADP is generated, and the
second is the non oxidative
synthesis of 5-carbon sugars .

4. The Oxidative Reaction
 Glucose-6-phosphate is converted to 6-phosphogluconolactone, and
NADP is reduced to NADPH H.
 Enzyme: glucose-6-phosphate dehydrogenase
 6-phosphogluconolactone is hydrolyzed to 6-phosphgluconate.
 Enzyme: gluconolactonase
 6-phosphogluconate undergoes an oxidation, followed by a
decarboxylation. Co2 is released, and a second NADPH H is generated
from NADP. The remaining carbons from ribulose-5 phophate.
 Enzymes: 6-phosphogluconate dehydrogenase

5. The Non Oxidative Reactions
 Ribulose-5-phosphate is isomerized to ribose-5-phosphate or
epimerized to xylulose-5-phophate.
 Ribose-5-phosphate and xululose-5-phosphate undergo
reactions, catalyzedby transketolase and transaldolase, that
transfer carbon units, ultimately forming fructose 6-phosphate
and glyceraldehyde-3-phosphate.
 Transketolase, which requires thiamine pyrophosphate,
transfer two-carbon units.
 Transaldolase transfers three-carbon units.

6. Overall reaction of the pentose
phosphate pathway
3 Glucose-6-P + 6 NADP 3 ribulose-5-P +
3co2 + 6 NADPH
3 Ribulose-5-P 2 xylulose-5-P + Ribose-5-P
2 xylulose-5-P + Ribose-5-P 2 fructose-6-P +
Glyceraldehyde-3-P