Regulation of Enzyme Activity

Summary

The video explains three main methods of regulating enzyme activity: allosteric control, covalent modification, and proteolytic cleavage. Allosteric enzymes can be regulated by molecules called effectors, either activating or inhibiting the enzyme. Covalent modification, such as phosphorylation, alters enzyme activity by modifying residues like tyrosine, serine, and threonine. Proteolytic cleavage activates enzymes from their inactive forms (zymogens), such as trypsinogen becoming active trypsin. The video discusses these mechanisms in detail, providing examples like ATCase for allosteric regulation and phosphorylase for covalent modification.

Takeaways

• 🔍 There are three main ways to regulate enzyme activity: allosteric control, covalent modification, and proteolytic cleavage.
• 🔑 Allosteric enzymes are regulated by molecules called allosteric effectors or modulators, which bind to the allosteric site.
• 🚫 Allosteric inhibitors bind to the allosteric site and distort the enzyme’s active site, preventing substrate binding.
• ⚡ Allosteric activators bind to the allosteric site and activate the enzyme by changing its shape to allow substrate binding.
• 📊 Allosteric enzyme graphs are sigmoidal and do not follow Michaelis-Menten kinetics.
• 🔁 Negative feedback regulation involves product molecules (like CTP) inhibiting enzyme activity to conserve resources.
• 🧬 Covalent modification involves changes like phosphorylation, acetylation, and methylation, which affect enzyme activity.
• 🧪 Phosphorylation involves adding a phosphate group to specific residues (tyrosine, serine, threonine), altering enzyme function.
• ⚙️ Kinases add phosphate groups to enzymes, while phosphatases remove them.
• ✂️ Proteolytic cleavage activates enzymes by cutting specific residues, converting inactive precursors into active forms.

Q & A

What are the three main ways to regulate enzyme activity?

The three main ways to regulate enzyme activity are allosteric control, covalent modification, and proteolytic cleavage.

What is allosteric regulation of an enzyme?

Allosteric regulation occurs when an enzyme's activity is regulated by a molecule called an allosteric effector, which binds to an allosteric site on the enzyme, altering its shape and function.

How does an allosteric inhibitor affect enzyme activity?

An allosteric inhibitor binds to the allosteric site of the enzyme, distorting the shape of the active site, preventing the substrate from binding, and inhibiting enzyme activity.

What is the role of an allosteric activator?

An allosteric activator binds to the allosteric site of an enzyme, changing its shape in a way that allows the active site to bind to the substrate, thereby activating the enzyme.

What is a common characteristic of an allosteric enzyme's reaction graph?

An allosteric enzyme's reaction graph is sigmoidal, meaning it does not follow traditional Michaelis-Menten kinetics.

What is covalent modification, and how does it regulate enzymes?

Covalent modification involves the addition or removal of chemical groups (e.g., phosphorylation, adenylation, acetylation) to enzyme residues, which alters the enzyme’s structure and activity.

Which amino acids are commonly phosphorylated during enzyme regulation?

The amino acids commonly phosphorylated during enzyme regulation are tyrosine, serine, and threonine, which have hydroxyl (-OH) groups that can be phosphorylated.

What is the role of kinases and phosphatases in phosphorylation?

Kinases add phosphate groups to enzymes, activating or deactivating them, while phosphatases remove phosphate groups, reversing the effect of kinases.

What is proteolytic cleavage, and how does it activate enzymes?

Proteolytic cleavage involves the cutting of an inactive enzyme precursor (zymogen) into an active enzyme by removing specific residues, such as in the activation of trypsinogen to trypsin.

What is a zymogen, and how is it different from a proenzyme?

A zymogen is an inactive precursor of proteases that needs to be cleaved to become active. A proenzyme or proprotein is the inactive form of other enzymes that are not proteases.