Which enzy me is irreversibly inhibited by aspirin?
**Core Concept**
Aspirin, also known as acetylsalicylic acid, is a nonsteroidal anti-inflammatory drug (NSAID) that exerts its therapeutic effects by inhibiting the enzyme responsible for producing prostaglandins. This enzyme is a key player in the inflammatory response.
**Why the Correct Answer is Right**
The correct answer is **Cyclooxygenase (COX)**. Aspirin irreversibly inhibits COX enzymes, specifically COX-1 and COX-2, by acetylating a serine residue at the active site. This leads to a permanent inhibition of the enzyme, resulting in a decrease in the production of prostaglandins and thromboxanes. COX enzymes catalyze the conversion of arachidonic acid to prostaglandin H2, which is then converted to other prostaglandins and thromboxanes. The inhibition of COX enzymes by aspirin reduces inflammation, pain, and fever.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because **Lipoxygenase** is the enzyme responsible for the production of leukotrienes, not prostaglandins. While lipoxygenase is involved in the inflammatory response, it is not the target of aspirin.
**Option B:** This option is incorrect because **Phospholipase A2** is an enzyme involved in the hydrolysis of phospholipids to release arachidonic acid, which is then converted to prostaglandins by COX enzymes. However, phospholipase A2 is not the target of aspirin.
**Option D:** This option is incorrect because **Glucocorticoid receptor** is a receptor that regulates the transcription of genes involved in inflammation, but it is not the target of aspirin.
**Clinical Pearl / High-Yield Fact**
Aspirin's irreversible inhibition of COX enzymes is a key mechanism of action that makes it a useful drug for the treatment of pain, inflammation, and fever. However, it also increases the risk of bleeding due to the inhibition of platelet COX-1, which is involved in the production of thromboxane A2.
**Correct Answer:** C. Cyclooxygenase (COX)