Enzymes and Enzyme analysis

Question 1

Enzymes contribute to over 40% of drug targets

name two examples of drug targets in enzymes

Answer 1

1. targetting enzymes involved in cellular communication, such as signalling cascades second and messenger regulation
2. targetting enzymes involved in catecholamine (neurotransmitter) synthesis

Question 2

enzyme drug action for communication via cellular messengers

briefly explain how drugs are used to enhance the effect of certain enzymatic chemical messengers

give an example of a drug used to alter cellular signalling involving acetylcholine esterase

Answer 2

drugs can be used as inhibitors to prevent the breakdown of chemical messengers

e.g. neostigmine and donepezil are acetylcholine esterase inhibitors

Question 3

targetting enzymes involved in catecholamine (neurotransmitter) synthesis

drugs can be used as substrates to boost the production of a desired product

give an example of a drug used as a substrate for an enzyme to boost the production of dopamine

Answer 3

L-dopa can be used as a drug to increase the production of dopamine, by supplying more L-dopa as a substrate more dopamine is produced.

Question 4

what are false substrates?

Answer 4

false substrates compete with the enzymatic binding site and produce a product

Question 5

what are suicide substrates and give an example of one

Answer 5

suicide substrates are mechanism-based irreversible inactivators of specific enzymes

e.g. β-lactam antibiotics such as amoxicillin which irreversibly inactivates transpeptidases, the enzyme responsible for forming the bacterial cell wall, this substrate, therefore, kills the bacteria

Question 6

what is the Michaelis-Menten analysis used for

state the formula, if you can ;)

Answer 6

• Used for measuring enzyme activity versus substrate concentration

Question 7

what does the Michaelis-Menten constant represent?

Answer 7

• the concentration of substrate that produces 50% maximal enzyme velocity (activity)

Km is related but not identical to affinity

Question 8

at equilibrium what does Kd equal?

Answer 8

Kd = K_off / k_on

Question 9

what does k_cat symbolise in this reaction?

what assumption do we make when deriving an expression for Km in this equation?

Answer 9

• The irreversible side of the reaction is modelled using k_cat - catalytic rate constant
• The assumption that [ES] does not change throughout the process

Question 10

what equation links Km, K_off, K_on and K_cat

Answer 10

Question 11

what is Ki and what equation can we use to obtain it from this graph

Answer 11

Ki is the affinity (potency) of the inhibitor

it can be obtained using this equation:

Question 12

we can also use competition curves to get values for the inhibitor affinity

what is the independent variable in this case

Answer 12

the inhibitor is the independent variable because we are varying [inhibitor] and keeping the [substrate] constant

Question 13

what is the IC50?

and how can it be obtained from a competition curve?

Answer 13

the concentration of inhibitor that inhibits 50% of the enzyme activity

IC50 can be read off the graph by drawing across from 50% enzyme activity and looking at the x-axis