The hexose monophosphate shunt: Overview

© Michael Palmer 2014

Reactions in the oxidative stage

© Michael Palmer 2014

Reactions in the sugar shuffle stage

© Michael Palmer 2014

Ketoses and aldoses in the HMS

© Michael Palmer 2014

The mechanism of transketolase

© Michael Palmer 2014

The mechanism of transaldolase

© Michael Palmer 2014

Why do we need both NADH and NADPH?

© Michael Palmer 2014

NADPH generation by malic enzyme

© Michael Palmer 2014

NADPH generation by transhydrogenase and NADP-linked isocitrate dehydrogenase

© Michael Palmer 2014

Uses of NADPH

1. synthesis of fatty acids and cholesterol

2. fixation of ammonia by glutamate dehydrogenase

3. oxidative metabolism of drugs and poisons by cytochrome P450 enzymes

4. generation of nitric oxide and of reactive oxygen species by phagocytes

5. scavenging of reactive oxygen species that form as byproducts of oxygen transport and of the respiratory chain

Nitric oxide synthase requires NADPH

© Michael Palmer 2014

Signaling effects of nitric oxide

© Michael Palmer 2014

Phagocytes use NADPH to generate reactive oxygen species

© Michael Palmer 2014

Scavenging of reactive oxygen species requires NADPH, too

© Michael Palmer 2014

Glucose-6-phosphate dehydrogenase deficiency

● X-chromosomally encoded—males more severely affected

● most patients are healthy most of the time—hemolytic crises occur upon exposure to drugs or diet components that cause enhanced formation of ROS

● manifest in red blood cells because these cells lack protein synthesis—no replacement of deficient protein molecules

● affords partial protection against malaria—similar to sickle cell anemia and other hemoglobinopathias

Vicia faba and favism

© Michael Palmer 2014

Redox cycling of isouramil

© Michael Palmer 2014

Malaria parasites detoxify heme by crystallization

© Michael Palmer 2014

Primaquine and glucose-6-phosphate dehydrogenase deficiency

© Michael Palmer 2014