Inhibition II

Question 1

What are tight-binding inhibitors?

Answer 1

Intermediates between reversible and irreversible inhibition

Question 2

What are the two interrelated properties under this topic?

Answer 2

Tightness of binding and slowness of dissociation

Question 3

The limit to the rate at which binding occurs is called __________

Answer 3

Diffusion limit

Question 4

What is a “diffusion limit”?

Answer 4

The rate at which molecules can diffuse to each other through solution

Question 5

True or False: the molecule can encounter the protein in a random way

Answer 5

False: the molecule has to encounter the protein in the correct orientation

Question 6

What is the measurement for almost all “on rates” in practice?

Answer 6

10⁸ Molar⁻¹ s⁻¹

Question 7

The rate constant (Ki) can be expressed in terms of k₋ᵢ / kᵢ. How can you increase the rate constant?

Answer 7

Increase k₋ᵢ

Question 8

What is the difference between k₋ᵢ and kᵢ?

Answer 8

k₋ᵢ is the dissociation or “off” rate

kᵢ is the association or “on” rate

Question 9

The normal assumption (e.g. when doing Michaelis-Menten kinetics) that concentrations of free and bound inhibitor concentration is the same does not apply under the ff conditions:
- kᵢ of >10 nM may be less than the concentration of the enzyme, which means that we are varying the inhibitor concentration at concentrations less than the enzyme

This produces ____________ plots

Answer 9

Non-linear

Question 10

What does linearizing data do?

Answer 10

Amplifies error and results in less accurate kinetic constants

Question 11

What is a “best fit”

Answer 11

A line or curve corresponding to a mathematical equation that is put through an experimental data set

Question 12

How does a computer perform a “best fit parameter”?

Answer 12

The computer tries to fit a line to the data by moving it minutely each time, thousands of times within a second or two. The computer stops moving the line, when it reaches the best “fit” which is calculated by the least error

Question 13

Why do we want to minimize error?

Answer 13

To get the most accurate and precise kinetic constants

Question 14

What is the difference between accuracy and precision?

Answer 14

Accuracy is how close you are to the real answer

Precision is how repeatable the data is between days, people, labs, etc.

Question 15

True or False: Variability in drug response for the same dose is undesirable

Answer 15

True

Question 16

What are non-specific irreversible inhibitors?

Answer 16

Catalytic poisons

Question 17

What do complexing agents such as EDTA do to buffers?

Answer 17

They act to sequester excess metal in the solution and protect the enzyme

Question 18

Give an example on how the knowledge on heavy metals can provide insights to enzyme properties

Answer 18

Poisoning by Mercury II almost always involves essential sulfhydryl groups, so one can infer that sulfhydryl groups are critical in an enzyme if Hg inhibits it

Question 19

Where does irreversible binding occur?

Answer 19

In an area close to or inside the catalytic site

Question 20

What happens when k₋ᵢ is bigger than k₂?

Answer 20

The derivations of it allow the inhibitor to be treated similarly to the M-M constant

Question 21

What happens when k₂ is bigger than k₋ᵢ?

Answer 21

It is a Non-First Order Kinetics

Question 22

What happens in pharmacology or toxicology when there is non-first order kinetics?

Answer 22

Almost always causes elevated levels of drug or toxin in the body, causing adverse drug reactions that includes death

Question 23

What is Mechanism-based Inhibition (Suicide Inhibition)?

Answer 23

It is an irreversible enzyme inhibition that almost always uses a prosthetic group or a coenzyme. They are overwhelmingly found in xenobiotic-metabolizing enzymes

Question 24

What are the inhibitors that fall under the Mechanism-based Inhibition (Suicide Inhibition)?

Answer 24

Drugs

Question 25

What are the restrictions concerning drugs that are suicide inhibitors?

Answer 25

• (The drug) cannot be used in a disease process that requires enzyme inhibition
• Limit their (drugs’) absolute dose levels
• Limit how long the drugs can be administered for