Regulatory enzymes (6.5)

Question 1

what is a regulatory enzyme

Answer 1

• enzymes that can respond to certain molecular signals that can increase or decrease their catalytic activity
• typically the first unique enzyme in a pathway is a regulatory enzyme (best place to regulate)
• affect the overall rate of the reaction pathway

Question 2

list the three main types of regulation

Answer 2

1. allosteric
2. covalent modification
3. proteolytic cleavage

Question 3

allosteric regulation

Answer 3

• reversible noncovalent binding of regulatory compounds
• modulator binding causes conformational change
• can be inhibitory or stimulatory
• active site and regulatory site may be on different subunits

Question 4

what is an allosteric modulator

Answer 4

• regulatory compounds that bind to allosteric sites in allosteric regualtion

Question 5

what is the difference between heterotropic and homotropic regulation

Answer 5

• in homotropic, the substrate acts as both the modulator and substrate
  
  • same binding acts as active site and regulatory site
• heterotropic has different molecules as substrate and modulator

Question 6

what does a sigmoidal shape of a curve on a plot of V0 vs. [S] indicate?

Answer 6

-allosteric regulation at a fixed [S] –> higher K0.5
- negative modulator is more sigmoidal
- active modulation has a nearly hyperbolic curve - increased activity at a fixed [S] –> lower K0.5

Question 7

describe covalent modification in terms of enzyme regulation

Answer 7

• covalent changes include phosphorylation, methylation, glycosylation, etc.
• change can occur on one or more amino acids of an enzyme
• change properties of an enzyme such as conformation, what the enzyme can interact with, etc.

Question 8

describe proteolytic cleavage in terms of enzyme regulation

Answer 8

• cleavage causes changes which expose the enzyme’s active site or allow catalytic activity

Question 9

Do allosteric enzymes obey Michaelis-Menten kinetics?

Answer 9

• no, they often have multiple binding sites that affect biding of the substrate

Question 10

what is allosteric feedback inhibition

Answer 10

• type of allostery where the final product of a pathways feeds back to regulate the enzyme earlier in the pathway
• not all feedback inhibition is through allostery (some regulate transcription)