ENZYME ACTIVE SITE

• 3-dimensional cleft where substrate can bind
• Substrate specificity: depends on atom arrangement in cleft

Lock and key

• Enzyme’s substrate fits perfectly into active site

Induced fit

• Active site conforms to substrate’s 3D shape upon binding
• Lock-and-key and the induced-fit are 2 models of substrate binding to active site

ENZYME REGULATION

Allostery

• Effector molecules bind to enzyme and change substrate binding affinity

Transcription

• Enzyme synthesis turned on or off to regulate production

Reversible covalent modification

• Enzymes can be phosphorylated (activation or deactivation)

Isozymes

• Different forms of enzymes can be used to affect reaction rates

Proteolytic activation

• Some enzymes have part of their sequence cleaved to become active

ALLOSTERIC REGULATION

• Effector molecule (inhibitor or activator) binds to effector site
• Effector site: distinct from active site