Lecture 16 - Enzyme kinetics, inhibition, control + Enzyme mechanisms

Question 1

_____ reactions can give more complex kinetics

Answer 1

bisubstrate

Question 2

what is the bisubstrate reaction equation?

Answer 2

E + A + B >< (EAB) > E + P + Q

Question 3

What does an inhibitor do?

Answer 3

-impede enzyme activity

Question 4

what are 2 classifications of enzyme inhibitors?

Answer 4

1. reversible inhibitors

2. irreversible inhibitors (inactivators)

Question 5

What is the equation for reversible inhibitors?

Answer 5

E + I >< EI

Kd = Ki = [E][I]/[EI]

Question 6

what are 3 types of inhibition?

Answer 6

1. classical competitive inhibition
2. uncompetitive inhibition
3. noncompetitive inhibition

Question 7

what is classical competitive inhibition?

Answer 7

S and I compete for same site on enzyme

Question 8

what is uncompetitive inhibition?

Answer 8

• I binds only to enzyme substrate complex

- preventing conversion of S to product

Question 9

what is noncompetitive inhibition?

Answer 9

• I can bind to either E or ES
• enzyme becomes inactive when I binds
• S can still bind to EI complex, but conversion to product is inhibited

Question 10

What are 3 variations of competitive inhibition?

Answer 10

1. product inhibition
2. transition state analog
3. nonclassical competition

Question 11

what is product inhibition?

Answer 11

-the product turns off the enzyme

Question 12

what is transition state analog?

Answer 12

-an inhibitor similar to the transition state complex hijacks the enzyme

Question 13

what is nonclassical competition?

Answer 13

-the binding site of an inhibitor to a different site turns off the enzyme

Question 14

competitive inhibition requires ______ [S] to saturate

Answer 14

higher

Question 15

what does competitive inhibition mean for Km? Vmax?

Answer 15

• Km gets bigger

- Vmax unchanged because sufficient S can compete away I

Question 16

What does noncompetitive inhibition affect?

Answer 16

• ES binding

- lowers the turnover

Question 17

How does noncompetitive/mixed inhibitors affect Km?

Answer 17

if I has same binding affinity Ki to both E and ES, Km would strictly remain unchanged

Question 18

What happens to Vmax during uncompetitive inhibition?

Answer 18

-inhibiting ES shuts down turnover reduces Vmax

Question 19

How does uncompetitive inhibition affect E and S?

Answer 19

-makes E bind S better

Question 20

What is the slope of the LB plot for uncompetitive inhibition?

Answer 20

Km/Vmax

Question 21

How do enzyme catalyzed reactions often occur?

Answer 21

in a chain

Question 22

How is efficiency maximized for in enzyme catalyzed reactions?

Answer 22

• rate of each step must be kept in sync

- requires control scheme

Question 23

what is the control scheme regulating enzyme activity?

Answer 23

1. feedback control (inhibition)

2. feed forward control (activation)

Question 24

What are 4 common regulation mechanism?

Answer 24

1. altering an enzyme’s expression
2. noncompetitive inhibition of an enzyme by its or its downstream products
3. allosteric control
4. covalent modification

Question 25

What is allosteric control?

Answer 25

regulating an enzyme’s efficiency by cooperativity

Question 26

what is covalent modification?

Answer 26

signaling an enzyme to turn on or off

Question 27

What does ATCase do in E. coli?

Answer 27

-regulated by allosteric effectors, CTP and ATP

Question 28

what are the kinetics of ATCase in the absence of allosteric effectors?

Answer 28

• sigmoidal

- sign of cooperativity

Question 29

What does ATCase catalyze?

Answer 29

-formation of carbamoylasparate from asparate

Question 30

the formation of carbamoylasparate is important because….

Answer 30

-this is the first step in teh biosynthesis of pyrimidines in the metabolic pathway of nucleotide synthesis

Question 31

• A in the form of ATP ________ ATCase

- C in the form of CPT ______ ATCase

Answer 31

• activates

- inhibits

Question 32

ATCase is an example of what?

Answer 32

-enzyme regulation by allosteric control

Question 33

what is ATCase composed of?

Answer 33

12 protein subunits

Question 34

what does binding of ATP or CPT to regulatory sites produce?

Answer 34

-large scale conformational transition

Question 35

_____ CPT binds preferentially to the ____ state

______ ATP binds preferentially to the _____ state

Answer 35

• inhibitor, T (inactive)

- activator, R (active)

Question 36

In eukaryotes, what is the most common covalent modification?

Answer 36

-phosphorylation of the -OH group in Ser, Thr, or Tyr by kinases

Question 37

what do kinases do?

Answer 37

-phosphorylation

Question 38

what do phosphatases do?

Answer 38

dephosphorylation

Question 39

What does glycogen phosphorylase do?

Answer 39

catalyzes the breakdown of glycogen in animals

Question 40

What is glycogen phosphorylase regulated by?

Answer 40

phosphorylase kinase