Other Reducing-Equivalent Transport and Oxygen-Consuming Systems

7 Other Reducing-Equivalent Transport and Oxygen-Consuming Systems 

In most cells, more than 90% of the oxygen utilized is consumed in the respiratory chain that is coupled to the production of ATP. However, electron transport and oxygen utilization occur in a variety of other reactions, including those catalyzed by oxidases or oxygenases. Xanthine oxidase, an enzyme involved in purine catabolism (Chapter 27), catalyzes the oxidation of hypoxanthine to xanthine, and of xanthine to uric acid. In these reactions, reducing equivalents are transferred via FAD, and Fe and Mo , while the oxygen is converted to superoxide anion (O2)  

D-Amino acid oxidase is a flavoprotein located in peroxisomes. D-Amino oxidases catalyze the oxidation of a D-amino acid to the corresponding keto acid  

The oxygen consumed during phagocytosis is utilized by a unique enzyme system termed the respiratory burst oxidase or NADPH oxidase. The oxidase generates superoxide anion (Oj), a one-electron reduced species, driven by intracellular NADPH, 

Superoxide anion is also the source of a number of other microbicidal oxidants. It functions as an electron donor and is converted to hydrogen peroxide by superoxide dis-mutase  

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