Question

Classify each phrase as describing a competitive inhibitor, uncompetitive inhibitor, or mixed (mixed noncompetitive) inhibitor. Note that K m refers to apparent K m .

Answer 1

Competitive inhibitors bind to the active site, uncompetitive inhibitors bind to the enzyme-substrate complex, and mixed inhibitors can bind to both the free enzyme and the enzyme-substrate complex.

Step-by-step explanation:

Competitive Inhibition:

Competitive inhibition occurs when an inhibitor binds reversibly to the active site of an enzyme, competing with the substrate for binding. The inhibitor is structurally similar to the substrate, but it cannot undergo the same chemical reaction. The inhibitor can dissociate from the enzyme, allowing the substrate to bind and catalysis to occur. Concentration-dependent inhibition is observed.

Uncompetitive Inhibition:

Uncompetitive inhibition occurs when an inhibitor binds reversibly to the enzyme-substrate complex, changing the conformation of the enzyme. This type of inhibitor has a distinct binding site from the active site and does not compete with the substrate. The inhibitor prevents the formation of the enzyme-substrate complex or slows down the product yield. Excess substrate cannot reverse the inhibitory effect.

Mixed (Noncompetitive) Inhibition:

Mixed inhibition occurs when an inhibitor can bind to both the free enzyme and the enzyme-substrate complex. It binds to a site that is distinct from the active site and alters the three-dimensional conformation of the enzyme. This inhibitor either inhibits the formation of the enzyme-substrate complex or slows down the product yield. It does not structurally resemble the substrate and is not in competition with the substrate for the active site.

Therefore, based on the descriptions provided, you can classify each phrase as describing a Competitive Inhibitor, Uncompetitive Inhibitor, or Mixed (Noncompetitive) Inhibitor.

Answer 2

Mixed inhibition refers to the combination of two reversible types of enzyme inhibition, competitive inhibition and non-competitive inhibition. The term mixed is used when the inhibitor can bind both the free enzyme and the enzyme-substrate complex. In mixed inhibition the inhibitor is in a different place from the active site where the substrate is found.

Mathematically, mixed inhibition occurs when both alpha and alpha-prime factors (introduced in the Michaelis-Menten equation representing competitive and non-competitive inhibition respectively) are present (they are larger than unity).

In a special case of mixed inhibition, the alpha and alpha-prime factors are the same, then non-competitive inhibition occurs.

With this type of inhibition Km depends on the affinity of the inhibitor to join E or ES and Vmax decreases.

Enzymatic inhibitors are molecules that bind enzymes and decrease their activity. Since blocking an enzyme can kill a pathogen or correct a metabolic imbalance, many medications act as enzyme inhibitors. They are also used as herbicides and pesticides. However, not all molecules that bind to enzymes are inhibitors; Enzymatic activators bind to enzymes and increase their activity.

The binding of an inhibitor can prevent the substrate from entering the active site of the enzyme and / or hinder the enzyme from catalyzing its corresponding reaction. The inhibitor binding may be reversible or irreversible. Normally, irreversible inhibitors react with the enzyme covalently and modify their chemical structure to the level of essential residues necessary for enzymatic activity. In contrast, reversible inhibitors bind to the enzyme in a non-covalent manner, resulting in different types of inhibitions, determined whether the inhibitor binds to the enzyme, the enzyme-substrate complex or both.

Many medications are enzymatic inhibitors, so their discovery and improvement is an active field of research in biochemistry and pharmacology. The validity of a medicinal enzyme inhibitor is usually determined by its specificity (its inability to bind to other proteins) and its potency (its dissociation constant, which indicates the concentration necessary to inhibit an enzyme). A high specificity and potency ensures that the medication will have few side effects and therefore a low toxicity.