Pentose Phosphate Pathway of Glucose Oxidation

Pentose phosphate pathway

pathway that oxidizes glucose 6-phosphate, producing pentose phosphates and NADH

Cells and Tissues that use the pentose phosphate pathway

- rapidly dividing cells use ribose 5-phosphate to make RNA, DNA, and coenzymes

- tissues that carry out extensive FA synthesis require the NADPH provided in this pathway

- tissues that actively synthesize cholesterol and steroid hormones require the NADPH provided by this pathway

Lactonase

catalyzes the hydrolysis of lactone to the free acid 6- phosphogluconate

6-phosphogluconate dehydrogenase

catalyzes the oxidation and decarboxylation of 6-phosphogluconate to form ribulose 5-phosphate and NADPH

Overall equation for the pentose phosphate pathway

glucose 6-phosphate + 2NADP+ + H2O ----> ribulose 5-phosphate + CO2 + 2NADPH + 2H+

Ribulose 5-phosphate epimerase

epimerizes ribulose 5-phosphate to xylulose 5-phosphate

First step in the pentose phosphate pathway

transketolase catalyzes the transfer of a two-carbon fragment from a ketose donor to an aldose donor

- yields sedoheptulose 7-phosphate

Second step in the pentose phosphate pathway

transaldolase catalyzes the condensation of a three-carbon fragment from sedoheptulose 7-phosphate and glyceraldehyde 3-phosphate, forming fructose 6-phosphate and the tetrose erythrose 4-phosphate

Third step in the pentose phosphate pathway

the second transketolase rxn forms fructose 6-phosphate and glyceraldehyde 3-phosphate from erythrose 4-phosphate and xylulose 5-phosphate

Fourth step in the pentose phosphate pathway

thiamine pyrophosphate (TPP) stabilizes a two-carbon carbanion in the transketolase rxn, and a protonated Schiff base stabilizes the carbanion in the transaldolase rxn

reductive pentose phosphate pathway

converts hexose phosphates to pentose phosphates