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BIOCHEmISTRY ``BIOCHEMISTRY—METABOlISM BIOCHEmISTRY ``BIOCHEMISTRY—METABOlISM SECTION II 79

Pentose phosphate Also called HMP shunt. Provides a source of NADPH from abundantly available glucose-6-P
pathway (NADPH is required for reductive reactions, eg, glutathione reduction inside RBCs, fatty acid
and cholesterol biosynthesis). Additionally, this pathway yields ribose for nucleotide synthesis. Two
distinct phases (oxidative and nonoxidative), both of which occur in the cytoplasm. No ATP is
used or produced.
Sites: lactating mammary glands, liver, adrenal cortex (sites of fatty acid or steroid synthesis), RBCs.

REACTIONS
Oxidative NADP + NADPH NADP + NADPH CO
(irreversible) 2
Glucose-6-P
i 6-Phosphogluconate Ribulose-5-P i
Glucose-6-P dehydrogenase
Nonoxidative Phosphopentose
(reversible) isomerase
Fructose-6-P i Ribose-5-P i
Transketolase, B₁

Fructose Nucleotide
1,6-bisphosphate synthesis

DHAP Glyceraldehyde-3-P
i

Glucose-6-phosphate NADPH is necessary to keep glutathione X-linked recessive disorder; most common
dehydrogenase reduced, which in turn detoxifies free radicals human enzyme deficiency; more prevalent
deficiency and peroxides.  NADPH in RBCs leads to among African Americans.  malarial
hemolytic anemia due to poor RBC defense resistance.
against oxidizing agents (eg, fava beans, Heinz bodies—denatured globin chains
sulfonamides, nitrofurantoin, primaquine/ precipitate within RBCs due to oxidative stress.
chloroquine, antituberculosis drugs). Infection Bite cells—result from the phagocytic removal
(most common cause) can also precipitate of Heinz bodies by splenic macrophages.
hemolysis; inflammatory response produces Think, “Bite into some Heinz ketchup.”
free radicals that diffuse into RBCs, causing
oxidative damage.

Glucose-6-P NADP + 2 GSH H O
2 2
(reduced)

Glucose-6-P Glutathione Glutathione
dehydrogenase reductase peroxidase

GSSG
6-phosphogluconolactone NADPH 2H O
2
(oxidized)

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