Enzymes and Their Activity Units

Biological catalysts that speed up chemical reactions by lowering activation energy.

Most enzymes are proteins, but some RNA molecules with catalytic activity are called ribozymes.

The substance that an enzyme acts upon in a chemical reaction.

These enzymes are produced and function within the cells, playing a role in metabolism.

These enzymes are synthesized inside cells but function outside of them, like in the digestive system.

The amount of enzyme that converts 1 micromole of substrate to product per minute.

The amount of enzyme that converts 1 mole of substrate to product per second.

A non-protein component that binds to an enzyme and is essential for its activity.

A tripeptide composed of glutamate, cysteine, and glycine. It acts as a hydrogen donor, like in the enzyme insulinase (insulin-glutathione transdehydrogenase), which inactivates insulin.

A water-soluble vitamin that acts as a powerful reducing agent. It carries hydrogen and is essential for enzymes like dopamine oxidase and polyphenol oxidase.

A lipid-soluble molecule with a structure similar to vitamin K. It acts as a hydrogen carrier in the electron transport chain, enabling cellular energy production.

A crucial coenzyme involved in important metabolic processes such as oxidative decarboxylation. It carries acyl groups of fatty acids, activating them for further reactions.

A form of vitamin B6 that acts as a coenzyme in crucial metabolic reactions like transamination, decarboxylation, and desulfuration of amino acids.

Enzymes that can act on several substrates that share a common chemical bond.

Enzymes that specifically act on only one optical isomer of a substrate, ignoring its mirror image.

Enzymes that are capable of acting on two different substrates in the same reaction.

An inactive form of an enzyme that can be activated when needed.

A segment of a polypeptide chain that masks the active site of a zymogen, preventing its activity.

Enzymes that catalyze oxidation-reduction reactions. They transfer electrons from one molecule to another.

A subgroup of oxidoreductases that use oxygen as a hydrogen acceptor, producing water or hydrogen peroxide.

A subgroup of oxidoreductases that cannot use oxygen as a hydrogen carrier. They rely on other coenzymes like NAD+ or FAD.

These enzymes move functional groups, including methyl, acyl, amino, or phosphate groups, from one molecule to another. Kinases, a key subclass, specifically transfer phosphate groups.

Enzymes that break down molecules by adding water across a bond. These enzymes are important in digestion, biosynthesis, and signal transduction.

These enzymes catalyze the breaking of bonds other than by hydrolysis, often forming a double bond. Examples include decarboxylases and aldolases.

Enzymes that convert one isomer to another. These isomers differ in their spatial arrangement (optical, geometric, or positional) and can significantly impact biological activity.

Enzymes that catalyze the joining of two molecules with the help of ATP. These enzymes are vital for synthesis reactions and building larger molecules.

An enzyme utilizing oxygen as an electron acceptor, resulting in the formation of hydrogen peroxide (H₂O₂). Examples include 1-L-aminoacid oxidase and 2-D-aminoacid oxidase.

An enzyme utilizing substrates without requiring the presence of oxygen. Examples include 1- Lactate dehydrogenase and 2-Succinate dehydrogenase.

A site on an enzyme that binds to a regulatory molecule, causing conformational changes in the enzyme's structure and affecting its activity, often at the active site.

A molecule that binds to an allosteric site on an enzyme, influencing its activity.

A type of allosteric regulation in which the end product of a metabolic pathway directly inhibits the activity of an enzyme earlier in the pathway. It's like a brake on the entire process.

An enzyme that can exist in multiple states, switching between active and inactive forms, often controlled by phosphorylation or dephosphorylation.

The addition of a phosphate group to an enzyme, often triggering a change in its activity.

The removal of a phosphate group from an enzyme, often causing it to become inactive.

The production of an enzyme can be controlled by the presence of inducers or repressors.

A substance that increases the synthesis of an enzyme, stimulating its production.

A type of inhibition that cannot be reversed by increasing the concentration of the substrate or removing the inhibitor. This means the inhibitor permanently binds to the enzyme, disabling its activity.

Examples of irreversible inhibitors include strong acids, heavy metals like mercury, and organophosphate compounds like pesticides. These substances can permanently damage enzymes, making them inactive.

Some irreversible inhibitors specifically target the active site of an enzyme by binding to a specific amino acid residue. For example, iodoacetic acid reacts with thiol (SH) groups, which are often found in the active site of enzymes.

Irreversible inhibitors can also act by blocking activators or coenzymes needed for the enzyme's function. For example, fluoride ions can precipitate calcium, which is required for the activation of clotting enzymes.

Anti-enzymes are substances produced by living cells that irreversibly inhibit the activity of specific enzymes. For example, the stomach lining secretes antipepsin to protect itself from the digestive enzyme pepsin.

Cyanide ions (CN⁻), azide ions (N₃⁻), and carbon monoxide (CO) are irreversible inhibitors that can bind to iron ions, which are essential for the activity of cytochrome oxidase, a vital enzyme in cellular respiration.

Isoniazid (INH), a drug used to treat tuberculosis, inhibits the activity of transaminases by binding to the coenzyme pyridoxal phosphate. This prevents the transaminases from carrying out their vital functions.

EDTA (Ethylene Diamine Tetr Acetic acid) is an irreversible inhibitor that chelates with magnesium and calcium ions, inhibiting the function of enzymes like enolase and kinases.