5.11
Colinesterasi: Distribuzione e Funzione
Le colinesterasi sono un gruppo di enzimi serina idrolasi che svolgono un ruolo cruciale nella degradazione degli esteri di colina. I due tipi primari…
Le colinesterasi sono enzimi che scindono gli esteri della colina. In base alla loro distribuzione e funzione, esistono in due tipi distinti: AChE, o vere colinesterasi e BuChEs, o pseudocolinesterasi.
Entrambi i tipi hanno subunità catalitiche globulari, che possono esistere come forme solubili dell'enzima. La forma legata degli enzimi ha i componenti catalitici ancorati alla membrana tramite subunità strutturali.
Gli AChE sono sintetizzati nel reticolo endoplasmatico ruvido e si trovano principalmente nei neuroni colinergici e nelle placche terminali postsinaptiche
Sono specifici per ACh ed esteri correlati. Gli AChE legati alle sinapsi colinergiche idrolizzano l'ACh rilasciato, terminando la sua azione.
D'altra parte, i BuChE sono sintetizzati nel fegato. I BuChE legati sono ampiamente distribuiti nell'organismo, mentre la forma solubile si trova nel plasma.
BuChE idrolizza la butirrilcolina, l'ACh e altri anestetici contenenti esteri. Regola anche la crescita dei neuroni e la proliferazione cellulare.
View the full transcript and gain access to JoVE Core videos
Q1: What are the two main types of cholinesterases and how do they differ?
Cholinesterases exist as two distinct types: acetylcholinesterases (AChEs), or true cholinesterases, and butyrylcholinesterases (BuChEs), or pseudocholinesterases. AChEs are specific for acetylcholine and related esters, while BuChEs are non-specific and hydrolyze butyrylcholine, acetylcholine, and ester-containing anesthetics. This substrate specificity difference reflects their distinct physiological roles in the body.
Q2: Where are acetylcholinesterases synthesized and located in the body?
Acetylcholinesterases are synthesized in the rough endoplasmic reticulum and are primarily found in cholinergic neurons and at postsynaptic end plates. The bound form anchors to neuronal membranes at cholinergic synapses, where it hydrolyzes released acetylcholine to terminate its action. Soluble forms are found in cerebrospinal fluid and help regulate free acetylcholine concentration.
Q3: What is the role of butyrylcholinesterase in drug metabolism?
Butyrylcholinesterase is synthesized in the liver and widely distributed throughout the body in bound form, while soluble forms circulate in plasma. The plasma form hydrolyzes acetylcholine and ester-containing anesthetic agents, leading to drug inactivation after administration. This makes BuChE crucial for metabolizing certain medications and regulating neurotransmitter levels.
Q4: How do soluble and bound forms of cholinesterases differ structurally?
Both cholinesterase types exist as soluble and bound forms. Soluble forms consist of a globular catalytic subunit found in cerebrospinal fluid or plasma. Bound forms link the catalytic unit to structural subunits that anchor the enzyme to membranes at neuronal synapses or neuromuscular junctions, enabling localized substrate hydrolysis.
Q5: What happens when acetylcholinesterase breaks down acetylcholine at the synapse?
Bound acetylcholinesterase at cholinergic synapses hydrolyzes released acetylcholine into choline and acetate, thereby terminating its neurotransmitter action. This enzymatic breakdown is essential for regulating cholinergic neurotransmission and preventing excessive acetylcholine accumulation. Understanding this mechanism is critical for studying indirect acting cholinergic agonists mechanism of action.
Q6: What additional functions does butyrylcholinesterase perform beyond acetylcholine hydrolysis?
Beyond hydrolyzing acetylcholine and ester-containing anesthetics, butyrylcholinesterase regulates neuronal outgrowth and cellular proliferation. This dual functionality makes BuChE important not only for neurotransmitter metabolism but also for developmental and cellular processes. Its widespread distribution in skin, brain, liver, and gut smooth muscles supports these diverse physiological roles.
Q7: Why is substrate specificity important for distinguishing acetylcholinesterase from butyrylcholinesterase?
Acetylcholinesterase shows high specificity for acetylcholine and related esters, making it ideal for precise synaptic regulation. Butyrylcholinesterase is non-specific and hydrolyzes multiple ester-containing compounds, including anesthetics. This specificity difference determines their distinct tissue distributions and clinical significance in drug metabolism and neurotransmission.