19: Enzyme Inhibition, Drugs Interfering with Enzymes

Enzymes can be inhibited by

small molecules, ions, drugs, toxic agents

IRREVERSIBLE inhibition involved _________ binding to the enzyme

covalent

REVERSIBLE inhibition involves ________________ binding

noncovalent

the irreversible form of enzyme inhibition is also called

suicide inhibition

an irreversible (suicide) inhibitor binds to the __________ ______ of the enzyme and forms a ___________ _________ through a _________ bond during the normal _______________ reaction

active site irreversible complex covalent catalysis

is the enzyme inhibition by

• aspirin

• penicillin

• fluorouracil

irreversible or reversible?

irreversible

what type of inhibitor

competes with the substrate for binding to the enzyme?

competitive inhibition

do competitive inhibitors only bind to the active site of the enzymes?

NO they can bind to the active site or an allosteric site which once bound will change the conformation of the active site blocking binding

statins are a type of

allosteric competitive inhibitor

they bind to an allosteric site changing the conformation of the active site

which inhibitor binds only to the enzyme-substrate complex?

does this prevent binding or catalysis?

uncompetitive inhibition

• catalysis

camptothecin is uncompetitive and binds to what complex?

topoisomerase I and DNA complex

only binds once DNA is in the active site of topoisomerase I

which inhibitors prevent the substrate from binding twhao the enzyme?

which inhibitors allow the substrate to bind to the enzyme but inhibit the catalysis reaction once the substrate is attached?

binding = competitive

catalysis = noncompetitive and uncompetitive

what is the difference and similarity between uncompetitive and noncompetitive inhibition?

difference= uncompetitive binds once the substrate is already attached to the enzyme while noncompetitive can bind to both the complex or directly to the enzyme before the substrate binds

similarity = both inhibit catalysis while competitive inhibits binding but undergoes the same catalysis reaction just not as often

which types of enzyme binding of reversible which are irreversible?

reversible = competitive, noncompetitive, uncompetitive

irreversible = suicide inhibitor binds covalently to the active site

doxycycline, a collagenase inhibitor (periodontal disease) is an example of what type of inhibitor?

non-competitive

do pure or noncompetitive inhibitors bind equally well to the enzyme with or without substrate bound?

pure non-competitive

Are pure non-competitive or mixed non-competitive inhibitor substrates decreasing turnover or binding?

pure noncompetive decreases binding

mixed turnover and binding

do pure or mixed noncompetitive inhibitors bind preferentially to either the free enzyme or the enzyme- substrate complex enzyme-substrate

mixed non-competitive

what do pure non-competitive inhibitors decrease?

what do mixed non-competitive inhibitors decrease?

pure = turnover number

mixed = turnover AND substrate binding

do competitive inhibitors increase or decrease the value of Km?

increase Km

since the substrate active sites are blocked it will take a lot more substrate to bind to the spots that are still open

what happens to the Vmax of enzymes that are competitively inhibited?

Vmax UNCHANGED

once a substrate binds the catalysis goes on like normal, BUT it is harder to bind

can competitive inhibition be overcome by a sufficiently high [S]?

YES

if excess substrate is available then they will bind to the enzymes that aren’t inhibited and cause the same effect they would if there was a normal concentration of [S]

How do noncompeititve inhibitors which can bind to either the complex or the free enzyme impact Vmax?

Vmax decreases

the enzyme can no longer reach its full potential as its catalytic function is disturbed by the inhibitor

How do noncompetitive inhibitors effect Km?

Km is not impacted as it does not take more substrate to bind to the enzymes

enzymes can bind normally to substrates, but they won’t react as strongly as they would

can non-competitive inhibitors be overcome by increasing the substrate concentration?

NO

it doesn’t matter how much substrate there is or how many bind to enzymes since the catalytic function is disturbed with or without them binding to each other

what happens to the vmax of enzymes that undergo uncompetitive inhibiton

Vmax is decreased as once the substrate/enzyme complex is formed and the uncompetitive inhibitor binds the catalytic action is decreased and it won’t reach its maximum rate

what happens to the Km of enzymes that undergo uncompetitive inhibition?

decreased bc/ it takes less substrate to make a reaction BUT the reaction is not as strong

the less free binding enzymes there are the greater affinity the substrate will have for the substrate (like follow the leader)

drugs that act by noncompetitive and noncompetitive mechanisms can be

equally potent and selective

what is one advantage of using a noncompetitive inhibitor over a competitive inhibitor?

noncompetitive wont be overcome by increased substrates

if there are enough substrates than the effect of the competitive inhibitor can be reversed as the increased substrates will bind to the enzymes whose catalytic effect is unaffected

how do the following impact Km and Vmax

• competitive

• noncompetitive

• uncompetitive

• high Km + unchanged Vmax

• unchanged Km + decreased Vmax

• low Km + decreased Vmax

_______ __________ and _______ _______ are the most likely to be targeted by drugs with a total of 1194 and 220 drugs and 667 and 189 targets

human protein

pathogen protein

with proteins are the MOST targeted by drugs?

G-protein coupled receptors

compounds produced by bacteria and fungi which are capable of killing or inhibiting competing microbial species

antibodies

penicillin was the first antibiotic produced by __________ ____________ discovered in 1928 by __________ _______

Penicillium mold

Alexander Fleming

penicillin works against bacterial infections caused by __________ and _________________

streptococcus and staphylococci (gram + )

how can the following be treated?

• gonorrhea

• pneumonia

• diptheria

• syphilis

how does treatment work?

penicillin

prevents the peptidoglycan wall of bacteria from being formed by inactivating bacterial transpeptidase causing bacteria to get lysed

how does penicillin work as an antibiotic?

how are humans safe from treatment?

penicillin IRREVERSIBLY inactivates the bacterial enzyme, transpeptidase, which is the last step of building the bacterial wall

humans don’t have cell wall and don’t need transpeptidase

what kind of inhibitor is penicillin and why?

suicide inhibitor

penicillin binds to the active site of transpeptidase and binds irreversibly

• B lactams (penicillin, monobactums, cephalosporins, carbapenems)

• ____________________

• ______________________

all work as antibiotics by disrupting the cell wall of bacteria

glycopeptides

lipoglycopeptides

erythromycin and chloramphenicol block the translation of bacterial mRNA by inhibiting which ribosomal subunit?

large subunit (50S)

aminoglycosides and tetracyclines block bacterial mRNA translation by inhibiting which ribosomal subunit?

small subunit (30S)

Asprin:

Asprin is made from the bark and leaves of which tree?

What was identified as the active ingredient of Aspirin which was found within the bark and leaves?

• willow

• salicylic acid

what modification was made to saliciyclic acid to make asprin?

what is the new name of salicylic acid after the modification was made (current name of aspirin)

why was this change made?

acetyl was added using a base and acetyl chloride (chloride leaving group)

salicylic acid —> acetylsalicylic acid

although salicylic acid led to pain relief, neutralization often irritated the stomach

is Asprin an irreversible or reversible inhibitor

irreversible

what does aspirin irreversibly bind to? how does this effect bacteria?

cycloOxygenase (COX)

prevents arachidonic acid from converting into prostaglandin H2 Synthase

blocks inflammatory response

the cyclogenase component of Prostaglandin H2 synthase (PGH2) contains a _____________ ________ from the membrane to the active site

how exactly does aspirin block cycloOxygenase (COX) ?

the acetyl group from aspirin binds to the serine of the hydrophobic channel of COX irreversibly blocking the active site

can salysiclic acid also inhibit COX like aspirin (acytelsalyciclic acid) can?

YES

BUT the acetyl group of aspirin makes is more effective

which protease can lead to AIDS and what does the protease do normally?

which drug is used to treat AIDS?

HIV- 1 protease

HIV replication

crixiVAN

which protease can lead stroke, vascular clots, and coronary infarctions?

how does the protease normally function?

which drugs can be used to treat symptoms?

thrombin

prevent blood from leaving out of damaged vessel

argatroban

which protease can lead to hypertension?

how does the protease normally function?

which drugs can be used to treat symptoms?

ACE

convert angiotensin 1 to angiotensin 2

PRILS

what type of inhibitors are ACE inhibitors?

competitive (bind to active site and prevent binding)

ACE converts angiotension 1 to 2

where is angiotensin 2 typicallly found?

does angiotensin increase or decrease blood pressure through vasodilation/constriction?

• angiotensin is a HORMONE found in the blood

• increase

• vasoconstriction

without ACE inhibitiors the heart muscle may become hyper/hypo trophied

hypertrophied (less open space for blood to fill in because of enlargeded heart muscles)

how is angiotensin normally able to be converted into angiotensin 2 using ACE

removes peptide bond through proteolysis

ACE is a

zinc metalloproteases (has zinc cofactor on active site)

which drug

• protects kidney function in patients with diabetes or mild kidney disease

• reduce heart attack in patients with diabetes

• prevent death from heart failure

• relax veins and arteries to lower blood pressure

competitive ACE inhibitors

thrombin coverts ________ to ___________

what step is this of anticoagulation?

fibrinogen to fibrin

LAST STEP

there is a fine line between hemorrhage and ___________ so the clotting process must be precisely regulated

thrombosis

an enzymatic cascade is a series of _______ activations —> rapid response

zymogen

the ___________ form of one clotting factor catalyzes the activation of the next _____________

at each step the signal is ________

how much amount of the initial factor is needed to trigger the cascade? because of this is clotting rapid or slow?

• activated zymogen

• activated

• only few intial factor is needed RAPID response so risk of thrombosis

which drugs are used to prevent

• stroke

• myocardial infarction

• pulmonary embolism in patients with increased clotting risk

anticoagulant drugs

what cofactor is on the active site of thrombin allowing it to convert fibrinogen into fibrin through hydrolysis?

serine

what are DTIs?

Direct Thrombin Inhibitors

what is the difference between univalent and bivalent anticoagulants?

Univalent: bind only to active site of thrombin

Bivalent: bind both to the active site and REGULATORY site of thrombin

which anticoagulation drugs are univalent? where do they bind to?

Argatroban + Melagatran

only bind to the active site of thrombin

which anticoagulation drugs are bivalent? where do they bind?

hiriudin and bivalirudin

bind to both the active site AND regulatory site of thrombin

Warfarin is a anticoagulation drug

Does it work as a direct thrombin inhibitor?

NO

does not bind to thrombin but prevents its synthesis by inhibiting enzymes needed for the synthesis of Vitamin K which synthesizes prothrombin

Warfarin is a _________ _____ antagonist

_______ ______ is used to synthesize __________

SO acts as Warfarin an indirect thrombin inhibitor

vitamin K

vitamin K is used to synthesize Prothrombin

how does warfarin act as a vitamin K antagonist?

blocks vitamin K epoxide reductase

____________ _________ cleaves multidomain viral proteins into their ACTIVE forms

HIV protease (aspartyl protease)

indinAVIR and retroVIR act as HIV protease inhibitors which prevents the virus from being infectious

they have also dramatically reduced deaths due to AIDS

how?

virus is only infectious if its proteins are ACTIVE

HIV protease cleaves viral proteins into their activated forms

If HIV protease is blocked then viral proteins are no longer activated

__________: one of the first HIV protease inhibitors developed

• designed to resemble a peptide substrate of the enzyme

• the OH group of the drug interacts with the two _________ residues of the active site of HIV proteases BUT does not block all of these sites on other enzymes

• indinavir

ASPARTARTE residues

does the OH group from Indinavir react with every enzyme that contains an aspartate group ?

NO

limited to only aspartate groups on the active site of HIV proteases

Paxlovid is a combination drug used to treat _________

what two drugs make up paxlovid?

covid

• nirmatrelvir and ritonavir

Which enzyme is blocked by nirmatrelvir?

What does the enzyme normally do?

What does ritonavir which is also apart of paxlovid do?

• 3CL protease

• allows covid to make copies of itself

• prolongs the stay of nirmatrelvir by blocking its metabolism by CYP450 CYP3A4 and as a pharmacokinetic boosting agent

how is paxlovid administered?

Paxlovid prevents _________

and reduces ___________ rate and ________

• orally

• transmission

• hospitalization mortality

Kinases transfer a _____ phosphate group from _______ to a ______ _______ or ________ residues of a protein

gamma ATP serine threonine tyrosine

phosphatases transfer the phosphate form a ____________ to a __________ molecule

phosphoprotein

water

there are more than 518 protein ____________ in the human genome making up about 1.7% of all human genes

they __________________ more than 30% of cellular proteins

kinases

phosphorylate

what are the three different types of kinases?

• serine-threonine

• tyrosine

• dual (serine, threonine, or tyrosine)

what was the first protein kinase to be inhibited? what did it treat?

Cyclosporine — allograft transplant

BCR-ALB

chronic myelogenous leukemia (CML)

what causes Chronic Myelogenous Leukemia?

Philadelphia Chromosome: translocation of Abl (tyrosine kinase--9) and BCR (22)

which TYROSINE kinase is inhibited by gleevac specifically to treat Chronic Myelogenous leukemia?

how does it inhibit the kinase?

Bcr-Abl kinase

occupies the ATP binding site so Kinase cannot take phosphate off of ATP to add to another protein on its tyrosine residue

besides the bcr-abl kinase, what other kinases can GLEEVAC inhibit?

• Tyrosine Kinase

  • c-Kit = GI tumors

  • P13K = solid tumors

  • EGFR = lung cancer

• Serine threonine Kinases

  • BRAF = melanoma

  • mTOR = renal tumors