## Core Concept
Entacapone is a drug used in the management of Parkinson's disease. It belongs to a class of drugs known as COMT (catechol-O-methyltransferase) inhibitors. The core concept here involves understanding the role of COMT in the metabolism of catecholamines, such as dopamine.

## Why the Correct Answer is Right
Entacapone works by inhibiting the enzyme catechol-O-methyltransferase (COMT). COMT is involved in the breakdown of catecholamine neurotransmitters, such as dopamine, norepinephrine, and epinephrine. By inhibiting COMT, entacapone increases the availability of dopamine in the brain, which helps to alleviate symptoms of Parkinson's disease. This mechanism is particularly useful when combined with other treatments like levodopa/carbidopa.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it does not specify the correct enzyme related to entacapone's mechanism of action.
- **Option B:** This option is incorrect for the same reason as Option A; it does not accurately represent the target of entacapone.
- **Option D:** This option is incorrect because it also does not accurately represent the enzyme that entacapone inhibits.

## Clinical Pearl / High-Yield Fact
A key point to remember is that entacapone and other COMT inhibitors are used as adjuncts to levodopa therapy in Parkinson's disease. They help extend the effectiveness of levodopa by preventing its conversion to 3-O-methyldopa, thereby increasing the availability of levodopa to cross the blood-brain barrier and increase dopamine levels.

## Correct Answer: C. Catechol-O-methyltransferase (COMT).