Chpt 7-Models for Enzyme Kinetics and classes of enzyme inhibitor drugs

Question 1

Enzyme kinetics help to do what?

Answer 1

1. Understand general cell metabolism
2. Understand inhibitor drug action
3. Design therapeutic agents

Question 2

Kinetic assays with enzymes are widely used in drug _____________.

Answer 2

discovery and development.

Question 3

What tests for the presence or absence of specific enzymes employ kinetics?

Answer 3

Clinical diagnostic

Question 4

Higher the [S] greater the [P] formation.
However, the ______ formation is indirectly
dependent on [E.S].

Answer 4

Product [P]

Question 5

What is explained in Michaelis-Menten Model?

Answer 5

1. Enzyme contacts substrate by DIFFUSION and forms the E∙S reaction intermediate.
2. Then E∙S passes over an activation barrier to yield product P
3. Or E∙S could fall apart and the enzyme and substrate diffuse away from each other.

Question 6

Enzyme contacts substrate by _________ and forms the E∙S reaction intermediate.

Answer 6

diffusion

Question 7

many enzyme-catalyzed reactions are reversible or irreversible?

Answer 7

Irreversible

Question 8

An ACTIVATED complex (E.S)‡ has no _______.

Answer 8

Stability. (unstable). It is the state at the highest free energy level (top) of the reaction progress diagram.

Question 9

How long does the activated complex last?

Answer 9

It lasts for only one or a few molecular vibration periods; about 10-15 sec.

Question 10

The (E•S) complex is generally much ______ compared to activated E•S and may last for quite some time.

Answer 10

Stable

Question 11

k−1 is the rate constant for the ___________. A uni-molecular reaction step.

Answer 11

dissociation of E∙S

Question 12

What is the rate constant for forming E∙S?

Answer 12

k+1. A bimolecular reaction step.

Question 13

k+2 is the rate constant for the breakdown of E∙S to form E + P. Also a ______ reaction step.

Answer 13

unimolecular

Question 14

This number defines the maximum number of substrate molecules converted

Answer 14

k+2 or kcat

Question 15

Apparent second-order kinetics gradually switches over to first-order kinetics when?

Answer 15

An unusual feature in enzyme kinetics: as the concentration of substrate increases

Question 16

When [S] is _____ by comparison to Km we have mostly free enzyme in the system

Answer 16

low

Question 17

When [S] is high, we have mostly enzyme with substrate in the ________

Answer 17

active site

Question 18

What is the first regime of substrate kinetics?

Answer 18

1. Mostly saturated enzyme
2. Depends only on [E0]
3. Maximal rate of reaction

Question 19

The higher the Km of an enzyme, the ________ its affinity for its substrate.

Answer 19

LOWER

Question 20

Mostly free enzyme, Depends on both [E] and [S], k+2 / KM appears to be an effective second-order rate constant defines what?

Answer 20

Second-order kinetics : [S] &laquo_space;Km

Question 21

The traditional unit (U) of enzyme activity is the amount of enzyme that can convert one micromole of substrate into products in one minute.

Answer 21

units of enzyme activity

Question 22

SI unit of activity is the katal (symbol kat), the amount of activity that converts one mole of substrate into products in one second.

Answer 22

units of enzyme activity

Question 23

How does many drugs function to inhibit key enzymes?

Answer 23

By blocking their action, a therapeutic effect is produced

Question 24

drugs “compete” with substrate, for access to the enzyme called

Answer 24

competitive inhibition

Question 25

Competitive inhibition effects the catalytic process. T or F?

Answer 25

False. A competitive inhibitor has no effect on the catalytic step; kcat or k+2 are the same.

Question 26

Formation of the E∙S complex is reduced while a new type of complex, E∙I, is formed.

Answer 26

This occurs in competitive inhibition

Question 27

The apparent Michaelis constant is numerically ________ than Km and it increases as the concentration of inhibitor rises.

Answer 27

Larger. when referring to competitive inhibition

Question 28

Can a higher concentration of substrate restore the original rate of reaction (overcome the inhibition) regarding competitive inhibition?

Answer 28

Yes

Question 29

The maximum velocity is still the same; Vmax does not change. T or F

Answer 29

True

Question 30

The E∙I and E∙S∙I complexes are both active or inactive for mixed and competitive inhibition?

Answer 30

Inactive

Question 31

For noncompetitive inhibition the inhibitor has the ________ affinity for either E or the E∙S complex

Answer 31

Same

Question 32

The irreversible inhibition of an enzyme entails ______ attachment of the inhibitor to the enzyme, or some covalent modification, involving key residues of the enzyme, by the inhibitor.

Answer 32

1. Covalent

Question 33

Many drugs that target enzymes are what kind of inhibitors?

Answer 33

Irreversible inhibitors of those enzymes like penicillin and aspirin

Question 34

Active-site directed irreversible inhibition are designed to do what?

Answer 34

These inhibitors are designed to attach covalently in or near the enzyme’s active site

Question 35

Suicide inhibitors are another class of _______ inhibitors

Answer 35

irreversible

Question 36

What kind of inhibition is describe as the inhibitor being unreactive until the enzyme attempts to use it as a substrate?

Answer 36

Suicide inhibitors

Question 37

Upon binding and undergoing few chemical changes the molecule becomes highly reactive and binds irreversibly with the enzyme. Thus the enzyme commits “suicide” by converting the compound.

Answer 37

Suicide inhibitors for example Penicillin, physostigmine, 5-fluorouracil

Question 38

Many enzymes have _______ groups that are needed either for catalytic activity, ___________ , or for structural reasons.

Answer 38

1. Sulfhydryl

2. Binding cofactors

Question 39

These sulfhydryl groups can form tight bonds with heavy metals such as mercury, lead, silver, even iron and copper.

Answer 39

Heavy Metal Toxicity

Question 40

Once the heavy metal atom is bound, the sulfhydryl cannot function in catalysis

Answer 40

Heavy Metal Toxicity

Question 41

This defines Enzymes as drug targets

Answer 41

Pick a key enzyme, inhibit it, reduce the concentration of the metabolites and/or buildup the concentration of substrate(s), and so get a clinically useful response.

Question 42

Give examples of Enzymes as drug targets

Answer 42

1. Statins inhibit HMGCoA reductase, leading to lower cholesterol levels.
2. Gleevec inhibits a protein kinase and blocks proliferation of cancer cells.
3. Aspirin inhibits a cyclo-oxygenase and reduces inflammation.

Question 43

Combine two inhibitors that target the same (or a related) pathway to get an enhanced response, greater than what might be achieved with either inhibitor alone. This is the definition of what?

Answer 43

Combination chemotherapy

Question 44

Give an example of combination therapy

Answer 44

Example: Co-trimoxazole is a very effective antibacterial combination of trimethoprim and sulfamethoxazole

Question 45

What are the four basic strategies of inhibitor design?

Answer 45

1. Mimic the substrate;
2. Mimic the transition state;
3. Irreversibly react with a key residue;
4. Change the enzyme’s conformation or state of assembly

Question 46

Substrate mimics are usually ______ inhibitors

Answer 46

competitive

Question 47

use compounds that have much but not all of the chemical features of the substrate, so that they fit into the active site and are held relatively tightly, but do not themselves react and do not let substrate react.

Answer 47

Substrate mimics

Question 48

Give an example of a substrate mimic

Answer 48

Examples: Ibuprofen and related compounds occupy the active site to inhibit prostaglandin synthase (COX) enzyme, and act as anti-inflammatory drugs

Question 49

Compounds can be made that ________ the transition state of substrate but that cannot go on to complete the reaction.

Answer 49

Resemble

Question 50

Transition state compounds

Answer 50

These compounds should bind more tightly to the enzyme than does the natural substrate

Question 51

Irreversible Inhibition

Answer 51

Aspirin acetylates a key serine residue in the active site of cyclo-oxygenase (prostaglandin synthase)

Question 52

Change the Enzyme’s Conformation or State of Assembly

Answer 52

The inhibitor might then interfere with binding of substrate in the correct conformation, or with catalysis in some way.

Question 53

Use an uncompetitive inhibitor that might bind to a different site on the enzyme, away from the active site.

Answer 53

Change the Enzyme’s Conformation or State of Assembly

Question 54

Another possibility is that the inhibitor could block the proper association of enzyme subunits.
Such inhibitors are much harder to discover and develop, and are not very common

Answer 54

Change the Enzyme’s Conformation or State of Assembly