Phagocytosis and the pentose phosphate pathway

The pentose phosphate pathway is crucial to the survival of erythrocytes because of its ability to provide NADPH for reduction of toxic, spontaneously produced oxidants. In phagocytic cells, the pentose phosphate pathway generates oxidizing agents that participate in the killing of bacteria and abnormal cells engulfed by the phagocytes. 

NADPH oxidase is thought to be an electron transport chain that includes a flavoprotein, and cytochrome bssg (Chapter 14). 

The NADPH is provided by the pentose phosphate pathway. Glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase are inhibited by NADPH at the concentrations found in the unstimulated phagocyte. As NADPH is consumed by NADPH oxidase, inhibition of the pentose phosphate pathway is reduced, increasing the rate of formation of NADPH. 

Phagosomes contain some of the activated NADPH oxidase from the cell surface, and superoxide is produced within the phagolysosome. Although superoxide is only bactericidal against organisms that lack superoxide dis-mutase, it is the substrate for formation of a number of cytotoxic compounds. 

Formation of phagolysosomes is accompanied by a decrease in the pH of their interior, which causes spontaneous conversion of superoxide anion to oxygen and hydrogen peroxide  

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