Pentose Phosphate Pathway - Biochemistry - Lecture Slides, Slides of Biochemistry

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Pentose phosphate pathway

So far we have discussed the glucose catabolism with major emphasis on generation of ATP. Oxidation of Glucose to carbon dioxide via glycolysis, PDC, CAC generates ATP and reducing equivalents such as NADH and FADH2 which are further oxidized in ETC generating ATP by oxidative phosphorylation.

Cells require ATP as well as reducing power for exergonic synthetic reactions. In most mammalian cells NADH produced by glycolysis and CAC is efficiently utilized by oxidative phosphorylation for ATP generation.

Thus the NAD+/NADH ratio is always around 1000 (i.e. high concentrations of NAD+). Therefore NADH is not the best reducing equivalent for synthetic reaction.

In order providing reducing power for synthetic reactions, cells produce NADPH in a special pathway of oxidation of glucose 6 phosphate called pentose phosphate shunt. NADP+/NADPH ration is 0.01 in most cells as it is not used in oxidative phosphorylation and it is available exclusively for reduction reactions required for synthetic purposes.

NADPH: an other currency for reducing power in synthetic reaction.

This pathway generates NADPH and Ribose-5-P which is used for

nucleic acid synthesis.

Regulation of pentose phosphate pathway

The major specific product of this pathway are NADPH and Ribose 5P

which are used as reducing power for synthetic reactions and nucleic

acid synthesis respectively.

Glucose 6 phosphate dehydrogenase (G6P DH) is the main enzyme

that controls the flux (overall rate) of this pathway.

G6P DH is strongly inhibited by NADPH. Thus if the NADPH

concentration decreases, the G6PDH is activated.

NADPH is used to generate

reduced glutathione (GSH).

GSH plays a critical role in

quenching the oxyradicals

in the cells.

If NADPH generation is

inhibited due to the

mutations in G6PDH, cells

become susceptible to

oxidative damage.

Malaria parasite is very

sensitive to Oxy-radicals,

and people with G6PDH

defect are resistant to

malaria as the parasite is

killed by oxy-radicals.