Following exposure to amyl nitrite, a patient is diagnosed with methemoglobinemia. What reaction primarily mediates this condition?

Methemoglobinemia is primarily mediated by the oxidation of the iron in hemoglobin from its ferrous (Fe2+) to ferric (Fe3+) state. When hemoglobin is oxidized, it loses its ability to effectively bind and transport oxygen, leading to reduced oxygen delivery to tissues. Amyl nitrite promotes this oxidation process, which increases methemoglobin levels in the blood.

In the context of the answer choices, oxidation is the key reaction responsible for this condition. The process involves the conversion of hemoglobin into methemoglobin, which is unable to carry oxygen, thus causing symptoms related to tissue hypoxia. This condition can be particularly dangerous, as methemoglobinemia can lead to cyanosis and other complications if not promptly treated.

Other processes such as dephosphorylation, glycolysis, and phosphorylation do not play a role in the pathophysiology of methemoglobinemia following exposure to substances like amyl nitrite, making oxidation the definitive and appropriate choice for understanding the reaction that mediates this condition.