[Comparative-enzymological study of cholinesterase of the Pacific squid Todarodes pacificus]

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Cholinesterases: Distribution and Function01:22

Cholinesterases: Distribution and Function

Cholinesterases are a group of serine hydrolase enzymes that play a crucial role in the breakdown of choline esters. The two primary types of cholinesterases are acetylcholinesterases (AChEs) and butyrylcholinesterase (BuChEs), which differ in their distribution, function, and substrate specificity. AChEs, also known as true cholinesterases, specifically hydrolyze acetylcholine, while BuChEs, often referred to as pseudocholinesterases, can hydrolyze various choline esters, including...
Indirect-Acting Cholinergic Agonists: Mechanism of Action01:18

Indirect-Acting Cholinergic Agonists: Mechanism of Action

Indirect-acting cholinergic agonists work by interacting with an enzyme called acetylcholinesterase (AChE) in the synaptic cleft. They can be reversible or irreversible inhibitors and have different effects on the enzyme.
Reversible inhibitors like edrophonium bind to a specific part of the enzyme called the anionic catalytic site. They form noncovalent bonds, which means they are not strongly attached to the enzyme. This creates a temporary and less stable enzyme–inhibitor complex, leading to...
Enzyme Inhibition01:30

Enzyme Inhibition

Inhibitors are molecules that reduce enzyme activity by binding to the enzyme. In a normally functioning cell, enzymes are regulated by a variety of inhibitors. Drugs and other toxins can also inhibit enzymes. Some inhibitors bind to the enzyme’s active site, while others inhibit enzymatic activity by binding to other sites on the protein structure.
Enzyme Kinetics01:19

Enzyme Kinetics

Enzymes speed up reactions by lowering the activation energy of the reactants. The speed at which the enzyme turns reactants into products is called the rate of reaction. Several factors impact the rate of reaction, including the number of available reactants. Enzyme kinetics is the study of how an enzyme changes the rate of a reaction.
Scientists typically study enzyme kinetics with a fixed amount of enzyme in the controlled environment of a test tube. When more reactant, or substrate, is...
Direct-Acting Cholinergic Agonists: Pharmacokinetics01:31

Direct-Acting Cholinergic Agonists: Pharmacokinetics

Direct-acting cholinergic agonists, such as synthetic choline esters and naturally occurring alkaloids, exert their effects by enhancing the actions of acetylcholine and stimulating the parasympathetic nervous system. Synthetic choline esters share structural similarities with acetylcholine. For example, they have a positively charged quaternary ammonium or onium group, contributing to their hydrophilic characteristics. As a result, they are poorly absorbed in the body through oral...