Pentose Phosphate Pathway

7 important questions on Pentose Phosphate Pathway

Where does the pentose phosphate pathway take place?

Cytoplasm

What is the function of the PPP?

It is a crucial source of NADPH for use in reductive biosynthesis as well as for protection against oxidative stress.

What is the product of phase I (the oxidative phase)?

Glucose 6-phosphate is converted into Ribulose 5-phosphate by glucose 6-phosphate dehydrogenase. The enzyme is highly specific for NADP+.
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How is the oxidative and nonoxidative phase of the PPP controlled?

- Oxidative: low levels of NADP+ limit the dehydrogenation of glucose 6-phosphate as it is needed as the electron acceptor. NADPH competes with NADP+ in binding the enzyme. This ensures that NADPH is not generated unless the supply needed for reductive biosynthesis or protection against oxidative stress is low.

- Nonoxidative: availability of substrates

Why is a glucose 6-phosphate dehydrogenase deficiency most acute in red blood cells?

They lack mitochondria and therefore have no alternative means of generating reducing power.

Glucose 6-phosphate dehydrogenase is required to maintain reduced glutathione levels to protect against oxidative stress and Heinz bodies (cross-linked hemoglobin molecules).

The PPP is their only source of NADPH.
Cells under oxidative stress need NADPH to reduce oxidized glutathione to monomeric glutathione.  NADPH serves as an electron donor to reverse an oxidation reaction (breaking S-S bridges

What does the PPP produce?

NADP and ribose (C5) for biosynthetic processes.

By what is PPP activity regulated?

The NADPH/NADP+ ratio

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