Lecture 10: Enzyme Regulation

Question 1

Ways to regulate enzyme activity

Answer 1

1. Allosteric control
2. Regulatory proteins
3. Reversible covalent modifications
4. Proteolytic activation

Question 2

Allosteric control

Answer 2

Non-covalent binding of an effector ligand at a regulatory/allosteric site

Question 3

Allosteric enzyme kinetic curves

Answer 3

Don’t follow Michaelis-Menten; typically sigmoidal due to positive cooperativity (smaller Km for larger [S])

Question 4

Classes of allosteric effectors

Answer 4

1. Homotropic
2. Heterotropic

Question 5

Homotropic allosteric effector

Answer 5

Substrate also acts as an allosteric effector, binding to an adjacent active site. Almost always increases activity.

Question 6

Heterotropic allosteric effector

Answer 6

Non-substrate effector; binds at “true” allosteric site, can increase or decrease activity

Question 7

Positive vs negative effector

Answer 7

Allosteric effector that increases vs. decreases activity

Question 8

How do allosteric effectors function?

Answer 8

Effector binding induces conformational changes; K class = Km change, V class = Vmax change, or can change both

Question 9

Allosteric enzyme characteristics

Answer 9

Typically oligomers; multiple subunits/active sites and have positive/negative cooperativity

Question 10

ATCase

Answer 10

Allosteric control example: has multiple catalytic + regulatory subunits, has T and R states with substrates and +/- effectors (aspartate, CTP, ATP)

Question 11

Regulatory proteins

Answer 11

Enzyme regulation through reversible protein interactions that stimulate or inhibit

Question 12

Regulatory protein examples

Answer 12

Stimulating: calmodulin activating MLCK

Inhibitory: PKA w/ pseudo-substrate subunits that occupy active sites reversibly

Question 13

Reversible covalent modification

Answer 13

Enzyme regulation by adding/removing charged groups, inducing conformational changes (e.g. phosphate, sulfate, acetate). Activation/inhibition depends on specific enzyme.

Question 14

Proteolytic activation

Answer 14

Enzyme is synthesized as an inactive precursor (proenzyme/zymogen) that requires cleavage of 1+ peptide bonds to be activated.

Question 15

Features of proteolytic activation

Answer 15

-Happens only once; irreversible
-Can be cleaved outside cell w/o energy

Question 16

Clotting cascade

Answer 16

Understand general mechanisms:
-Cascade of zymogen activations
-Signal amplification with each step
-Creates rapid trauma response

Question 17

How does heparin affect the clotting cascade?

Answer 17

Heparin is an anticoagulant that irreversibly inactivates thrombin via antithrombin III

Question 18

How does warfarin affect the clotting cascade?

Answer 18

Warfarin is an anticoagulant that inhibits prothrombin synthesis (longer term effect)

Question 19

How does tPA affect clotting?

Answer 19

tPA is a clot buster; it activates plasminogen to degrade fibrin clots.