What conversion is inhibited in neutrophils and monocytes due to NADPH deficiency?

The correct answer focuses on the role of NADPH in the immune response, particularly in neutrophils and monocytes. NADPH is crucial for the function of the enzyme NADPH oxidase, which is responsible for the conversion of molecular oxygen to superoxide anions. This process is a key step in the respiratory burst that occurs when neutrophils and monocytes encounter pathogens. The superoxide radicals generated help mediate the destruction of microbial invaders.

A deficiency in NADPH would lead to reduced production of reactive oxygen species, thereby compromising the ability of these immune cells to effectively kill bacteria and other pathogens. This is particularly relevant in conditions such as chronic granulomatous disease, where patients experience recurrent infections due to this impaired ability to produce superoxide radicals.

In contrast, the other choices pertain to different metabolic pathways that do not involve the direct role of NADPH in the conversion of oxygen to superoxide. Glucose to pyruvate involves glycolysis, urea to ammonia relates to the urea cycle, and fatty acids to acetyl-CoA involves fatty acid oxidation. None of these processes are affected by NADPH availability in the same way that the production of superoxide is in neutrophils and monocytes.