Lecture 5: Regulation of enzymes

Question 1

Michaelis-Menten

Answer 1

Vi=Vmax(S) / Km+ (S)

Determines changes in velocity

Question 2

Benefit of Lineweaver-Burke plot 1/v

Answer 2

Requires less points to make a plot.
Make the extrapolation easier.
Km (x) and Vmax (y) can be calculated from the x and y intercepts

Question 3

Benefit of high Km (low affinity) in glucokinase?

Answer 3

Promotes glucose storage in liver

Question 4

Reversible vs irreversible inhibitors

Answer 4

Reversible inhibitors bind to enzyme through noncovalent bonds – enzyme can regains activity through dilution or addition of more substrate.

Irreversible inhibition – enzyme does not regain its activity upon dilution.

Question 5

Competitive inhibition

Answer 5

Vmax does not change
Km is increased - (less affinity)
Plot - lines intercept at y axis (same Vmax)

Substrate binds at same site as inhibitor
ex. Statin drugs competitively inhibit Hmg-CoA reductase that results in a decreased cholesterol synthesis

Question 6

Noncompetitive inhibition

Answer 6

Vmax is decreased
Km does not change - (same affinity)
Plot lines intercept at x axis (same Km)

Substrate binds at different site than inhibitor

Question 7

Feedback inhibition

Answer 7

Feedback inhibition is the phenomenon where the output of a process is used as an input to control the behavior of the process itself, oftentimes limiting the production of more product.

Question 8

Covalent modifications

• Phosphorylation
• ADP-ribosylation

Answer 8

-Phosphorylation - most common, activates or inactivates proteins.
ADP-ribosylation - causes cholera (dehydration) and pertussis (hypoglycemia)

Question 9

Allosteric enzymes

Answer 9

Enzymes that change their conformation upon binding an effector. Allosteric effectors promote or inhibit conversion from one conformation to another. Can be noncompetitive

Question 10

Example of allosteric regulated enzyme

Answer 10

Phosphofructokinase-1

• it is the major regulatory enzyme in glycolysis.
• It catalyzes the irreversible transfer of a phosphate from ATP to fructose-6-phosphate.
• It is allosterically activated by fructose 2,6-bisphosphate, which is produced in response to insulin.

Question 11

Advantages of allosteric regulators

Answer 11

• Stronger effect than competitive and noncompetitive inhibitors.
• May act as activators (don’t occupy active site).
• Do not require to resemble S or P.
• Effect is rapid, as concentration changes in the cell.

Question 12

example of protein-protein interaction

Answer 12

Protein kinase A (PKA) regulates a number of metabolic pathways.

Question 13

feed forward regulation example

Answer 13

glucose storage