Pentose Phosphate Pathway

Question 1

The PPP is a major source of what important shuttle?

Answer 1

NADPH

Question 2

What are the major roles of PPP?

Answer 2

NADPH supply
Oxidation (prevent oxidative stress)
Major route for glucose metabolism
Xenobiotics
Scrambling carbons (glycolysis)
Nucleotides

Question 3

What is the overall reaction of the PPP?

Answer 3

G6P + 2(NADP+) + water —-> Ribose-5P + 2NADPH + 2(H+) + CO2

Question 4

What are the three major phases of the PPP?

Answer 4

Oxidative (tissue distribution & reactions)
G6P —> Ribose-5P

Non-oxidative (reactions)
Ribulose-5P —> Ribose-5P
—-> Xyulose-5P

Scrambling (allows for metabolizing excess Ribose-5P

Question 5

What are the three major differences between PPP and glycolysis?

Answer 5

Glycolysis PPP
Shuttles: NAD+ NADP+
ATP: Net ATP No ATP
Products: Pyruvate (3C) Ribose-5P (5C)

Question 6

What is the regulatory step of the PPP and how is it regulated?

Answer 6

The first step, glucose-6-phosphate dehydrogenase.
G6PD catalyzes the oxidation of G6P where the electron acceptor is NADP+.

The concentration of NADP+ and NADPH in the cytosol influence flux.

If NADPH is being converted to NADP+ at a high rate, the level of NADP+ rises and increases the flux of G6P through the PPP.

If levels of NADP+ drop due to low demand of NADPH, PPP slows and G6P fuels glycolysis.

Question 7

What are the two possible modes of the PPP?

Answer 7

Mode I - cellular division - kicks in when cell needs to divide

Mode II - Fatty acid synthesis - kicks in when cell needs to make more NADPH