Chapter 15 Enzyme Specificity and Regulation

15.1 Specificity Is the Result of Molecular Recognition

15.1.1 Enzyme Specificity

• Structural specificity• Stereospecificity

15.1.2 Hypothesis of Enzyme Action

• the “lock and key” hypothesis

• the “induced fit” hypothesis

15.1.3 Active Site of Enzyme

The specific site on the enzyme where substrate binds and catalysis occurs is called the active site.

15.2 Allosteric Regulation

Feedback inhibition (or regulation)

A B C D ZE1 E2 E3 En

A B C

D Y

E Z E1 E2

E3 E4 En

E3*E4* En*

Sigmoidal curve

Allosteric activator Allosteric inhibitorCO2 + Glu + ATP

CTP

N-carbamoylaspartate

Asp ATCase

Carbamoyl phosphateActivation

Inhibition

15.3 Reversible covalent modification

15.4 Proteolytic Activation

15.4.1 Pancreatic Proteases

Trypsinogen

Enteropeptidase

Trypsin

Chymotrypsinogen Proelastase

Chymotrypsin Elastase

15.4.2 Blood Clotting Cascade

15.5 Regulation of Enzyme Synthesis and breakdown15.6 Isozyme