Enzyme Inhibition

Front 1

How does enzyme inhibition work?
the ligand _______ and ________ catalysis

Back 1

The ligand binds and diminishes catalysis

Front 2

When does irreversible enzyme inhibition occur?

Back 2

Ligand does not dissociate before the protein degrades or the patient dies
Inhibitor may bind covalently

Front 3

Is ibuprofen reversible or irreversible?

Back 3

It is reversible, binds to COX and is excreted within 24 hours when dissociated (associates and dissociates readily)

Front 4

Is aspirin reversible or irreversible? Why?

Back 4

It is irreversible, binds and takes a really long time to dissociate

Platelets only live for an average for 7 to ten days:: aspirin doesn't dissociate before the platelet is destroyed

Have to wait at least ten days before full clotting abilities of patient is restored

Front 5

Explain how penicillin is an irreversible enzyme inhibitor

Back 5

Enzyme glycopeptidyl transferase is responsible for linking two peptidoglycans to make bacterial cell wall construction. Penicillin resembles transition state analogue of the process

AND it binds more tightly than the normal substrate, and the crosslinking doesn't occur and the bacteria cannot withstand osmotic pressure and reverse

Front 6

Why is Augmentin needed in regards to penicillin's efficacy in the body?

Back 6

The enzyme beta-lactamase hydrolyzes penicillin::penicillin resistant
Happy to react with penicillin and get rid of it before it can do it's magic to inhibit the glycopeptidase reaction

Ne penicillins are made to be poor substrates for beta lactamase OR beta lactamase can be irreversibly inhibited by clavulinic acid aka augmentin.

Front 7

What are serpins? How does it affect serine protease activation?

Back 7

Serine protease inhibitors
irreversible "suicide" inhibitors
Naturally occurring in the body

Serpin protein cleavage site recognized by specific proteases
Serpin is a trap::when it reaches the covalent intermediate step, the serpin irreversibly changes conformation

Takes protease and slams it into the opposite direction

So the protease can't reverse or be hydrolyzes, as the force of the chain is strong enough to strain and deform the protease so it can't do anything

Balances the fact that serine proteases are irreversibly activated anyways (one serpin to one protease, and both DIE)

Front 8

What are some clinically important serpins?

Back 8

Anti-thrombin: inhibits coagulation in blood clotting cascade
alpha1-antitrypsin:: inhibits neutrophil elastase in lungs

Also, fibrinolysis, inflammation, apoptosis, etc. are regulated by serpins

Front 9

How do heavy metals act as poisonous irreversible inhibitors? What are two examples? How do you treat it?

Back 9

They have nonspecific binding to side chains::mercury binds sulfhydryl groups of cysteine

Mimic co-factor::lead mimics calcium, inhibiting calmodulin and protein kinas C

Treatment:chelation give pt another molecule that will outcompete and bind::speed up dissociation to cause inhibitor to release before patient dies

Side effects for calcium EDTA: MMPs might also be inhibited

Front 10

How is diabetes affected by irreversible inhibitors?

Back 10

Nonspecific glycation occurs on many level that destroys the activity of many enzymes and proteins, including glutathione reductase and G-6-P dehydrogenase

Blocks active sites, block conformational changes, redox conditions drastically altered, Loss of NADP+ for other reactions

Front 11

What are the three classes inhibitor effects on enzyme function are divided (based on how they affect activity curves)

Back 11

Competitive, non-competitive, uncompetitive

Front 12

How can you tell if it is an irreversible or reversible inhibitor?

Back 12

You try to diffuse away the inhibitor, and if you can still recover the enzymatic activity,than it is reversible

Front 13

What is the slope in a LIneweaver-Burke Plot? The y-intercept? The x-intercept?

Back 13

Km/Vmax
Y-intercept: 1/Vmax
X-intercept: -1/Km (extrapolations)

Front 14

What is competitive inhibition? What does it affect?

Back 14

Compete with substrate for the same form of the enzyme, often the same site

Affects Binding STEP, NOT catalysis
Affects Km (x intercept and slope of the line) if you're ONLY affecting the binding
Vmax is NOT affected (stays the same)
Km doesn't really change, it just appears to

Ki=rate of inhibition

Front 15

What are the three substrates for alcohol dehydrogenase? What should you do if someone drinks antifreeze and why?

Back 15

Ethanol, methanol, ethylene glycol (antifreeze)

If you add more ethanol/alcohol in excess, competitive binding will occur so that the antifreeze will not metabolically react and kill you::ethanol is used as a competitive inhibitor

Front 16

What occurs in noncompetitive inhibition? On a graph what does it affect? What doesn't it affect? How does it look on a Lineweaver-Burke Plot

Back 16

Substrate and still bind, despite the presence of the noncompetitive inhibitor binding, but the enzyme can't do anything with it::UNIFORMLY removes enzyme from the possibility of reacting

Interact with enzyme AND enzyme substrate complex

Affects Vmax::lowers enzyme concentrations
Km=[S] DOES NOT change (x value does not change)

Lineweaver-Burke:Y-intercept changes (Vmax is changing), but the Km stays the same

Front 17

What is used to noncompetitively inhibit heme oxygenase?

Back 17

Heme usually breaks down by the enzyme HO to CO and iron ion and vilirubin (normally a stress-response enzyme), seems to be upregulated in tumors

So use ketoconazole (drug) as an HO inhibitor

Front 18

Irreversible inhibitors can look like non-competitive inhibitors, how can you discriminate between the two?

Back 18

See if you can dilute it away::irreversible cannot unbind fast enough

Front 19

What is affected on the graph for non-competitive inhibitors? what does the lineweaver-burke plot look like? What is the drug example for it?

Back 19

Vmax, but NOT km

Different y-intercepts aka Vmaxs
Different Kms? not really a good conceptual model for it:: PARALLEL LINES

Ketamine anesthetic is an example of uncompetitive inhibition

Front 20

What is acetylcholinesterase? How does it come into play in the synapses?

Back 20

It is a hydrolase located in nerve synapses::active site similar to serine protease (has the catalytic triad)

Reversibly inhibited by carbamates (drugs and pesticides)
Irreversibly inhibited by (nerve gas and pesticides malathion and parathion)

Presynaptic neuron releases acetylcholine, which binds to receptors, acetylcholinesterase hydrolzyes acetylcholine very quickly::gets rid of excess acetylcholine to reset process

Serine has a hydroxyl group to form a covalent intermediate that binds to active site to form OAcetyl, with choline as a leaving group::water comes in and hydrolyzes the oacetyl to restore enzyme

Takes place in microseconds

Front 21

In myasthenia gravis, what happens in the synapse? In glaucoma? How do you fix it?

Back 21

MG: too few receptors
Glaucoma: symptoms alleviate when signal persists for normal receptors

To treat: inhibit acetylcholinesterase to allow more substrate to make it to the receptors (existing receptors can signal for a little bit longer)

Front 22

How do carbamates act as drugs as inhibitors for acetylcholestinase? why can you not have large concentrations of it?

Back 22

Slows enzyme down to 20 minutes from microseconds::neostigmine competes with acetylcholine for the hydroxyl on the serine, which makes the second step hydrolysis a lot slower

Carbamates can also act as poisons in high concentrations (nerve signal is overstimulated and then paralyzed)

Front 23

Patient had overdoes of carbamate (take out too much acetylcholine) Nerve signal overstimulated and then paralyzed. How do you treat it?

Back 23

Atropine: competes with receptors::doesn't send signal that acetylcholine does, so it alleviates the carbamate consequences

Irreversible inhibitor

Front 24

What is a reversible inhibitor in regards to acetycholine receptors that is a poison? How can you fix this and what is aging?"

Back 24

Organophosphates::poison::reaction causes the formation of a phosphoryl group, in which the hydrolysis takes days
Plus, another chemical reaction occurs: aging (can act faster than hydrolysis--minutes to hours)::lose OR group and is replaced, which is permanent, and cannot be hydrolyzed anymore

Wait for body to make more, which can take 2 weeks to 3 months::Little window of opportunity: if you have 8 hours to age, then you can bring in something that will speed up last hydrolysis step i.e. 2Pam aka pralidoxime which is a stronger nucleophile than water

not irreversible anymore (if you can get drug to pt before pt dies) which is why military people get atropine and 2PAm, but you want to make sure you were exposed BEFORE you take the 2PAM