Acetylcholine is rapidly inactivated at the neuromuscular junction. Which enzyme is primarily responsible for this degradation?

Explanation

## Acetylcholine Metabolism at the Neuromuscular Junction **Key Point:** Acetylcholinesterase (AChE) is the primary enzyme responsible for rapid inactivation of acetylcholine at cholinergic synapses, including the neuromuscular junction. ### Enzyme Localization and Function **High-Yield:** AChE is located in the synaptic cleft and on the postsynaptic membrane. It hydrolyzes acetylcholine into choline and acetic acid within milliseconds, terminating neuromuscular transmission. ### Comparison of Acetylcholine-Metabolizing Enzymes | Enzyme | Substrate | Location | Clinical Significance | |--------|-----------|----------|----------------------| | Acetylcholinesterase (AChE) | Acetylcholine | Synaptic cleft, postsynaptic membrane | Primary inactivator at NMJ and CNS | | Pseudocholinesterase (BChE) | Succinylcholine, mivacurium | Plasma | Metabolizes certain drugs; genetic variants affect drug metabolism | | MAO | Monoamines (dopamine, serotonin, norepinephrine) | Mitochondrial membrane | Does NOT metabolize acetylcholine | | COMT | Catecholamines | Cytoplasm | Does NOT metabolize acetylcholine | **Mnemonic:** **ACE = Acetylcholine-Cholinesterase-Enzyme** — The primary enzyme for acetylcholine inactivation. **Clinical Pearl:** Cholinesterase inhibitors (physostigmine, neostigmine, pyridostigmine) work by blocking AChE, prolonging acetylcholine's action at the synapse. This is therapeutically useful in myasthenia gravis but can cause cholinergic crisis if overdosed. [cite:KD Tripathi 8e Ch 6-7]