Enzymes (Inhibition)

What is the difference between reversible and irreversible inhibition?

• Irreversible → Inhibitor forms covalent bonds with enzyme

• Reversible → Inhibitor forms weak bonds with enzyme

What do competitive inhibitors do?

• Bind to an enzyme and prevent substrate molecules from binding to the enzyme active site

• Reduces the availability of enzyme active site for substrate binding → Reduces the rate of reaction

What are characteristics of competitive inhibition?

• Bind reversibly to the active site

• Bonds involved are weak, non-covalent bonds

• Similar conformation to the substrate → Compete with substrate

How can competitive inhibition be overcome?

Increase substrate concentration → Increase the chances of substrate binding instead of inhibitor binding

What do non-competitive inhibitors do?

• Alters the conformation of the specific enzyme active site → Substrate cannot bind to the active site in the correct orientation → Rate of reaction is decreased

• Decrease the availability of enzymes by forming inactive enzyme-inhibitor complexes

Where does the non-competitive inhibitor bind?

A site other than the enzyme active site ← Inhibitor bears no structural similarity to the substrate molecule

What are allosteric enzymes?

• Enzymes that consist of 2 or more subunits

• Each subunit has

  • Active site → Binds substrates

  • Allosteric site → Binds inhibitors or activators

How many conformational states can allosteric enzymes exist in and how are they stabilized?

• Active conformation → Binding of allosteric activator at the allosteric site

• Inactive conformation → Binding of allosteric inhibitor at the allosteric site

What is cooperativity in allosteric regulation?

Binding of a substrate to the first subunit → Changes the conformation of other subunits → Easier to accept subsequent substrates

What is feedback / end-product inhibition?

When a metabolic pathway is inhibited by the binding of the end product to an enzyme that acts early in the pathway

• End product may bind to the allosteric site of the enzyme → Alter shape and conformation of the specific enzyme active site → Substrate cannot bind → Rate of reaction decreased

• Prevents the waste of resources in producing excess product