exam #1 Flashcards
explain Vmax and Km
Vmax (a constant) - the theoretical maximum rate at which a enzyme can turn substrate into produce
Km (a constant) is 1/2 the Vmax
high Km means weak binding, low Km means tight binding
the higher the substrate concentration, the faster the reaction rate (V)
what do enzyme catalysts do?
reduce activation energy required, increasing the rate of reaction
For an enzyme that follows Michaelis-Menton kinetics, Km is equal to which of the following:
a. the [s] at one-half Vmax
b. the Vi at one half Vmax
c. The [s] at one-half Vi
d. The Vi at one-tenth Vmax
e. Two times the Vmax
a. the [s] at one-half Vmax
what is the Lineweaver-Burk Transformation?
inverse of the velocity curve slope of the line = Km/Vmax the y intercept is i/Vmax X intercept is -1/Km 1/V = Km/Vmax(1/S) + 1/Vmax
What are the two categories of enzyme inhibitors?
Reversible inhibitor: interact with enzyme via noncovalent associations
Irreversible inhibitor: interact w/enzyme via covalent associations
What are the classes of reversible inhibition?
competitive inhibitors: bind only to E, not to ES: bind to active site & compete with natural substrate for that site
noncompetitive inhibitors: bind either to E and/or to ES: bind to allosteric sites and alter structure so substrate doesn’t bind as it did naturally
How do the saturation curves for an enzyme catalyzed reaction change with different types of inhibitors?
with competitive inhibitor, Vmax stays the same, but there is a different Km (Km is larger)
noncompetitive inhibitor, Km stays the same, but Vmax is lower
how can you reverse the effect of a competitive inhibitor?
increase substrate concentration
By looking at a lineweaver-Burk Transformation graph (the one with straight lines, not the curve), how do you tell what kind of enzyme has been used?
Competitive inhibitor: the slope of the reaction with the inhibited enzyme is steeper than the uninhibited reaction. The two lines intersect on the Y axis which is the 1/Vmax point (because Vmax doesn’t change with a competitive inhibitor)
Noncompetitive inhibitor: Inhibited slope is still steeper than the uninhibited slope, but the lines intersect on the X axis (-1/Km) because Km stays the same and Vmax is reduced.
Describe mixed inhibition
Mixed inhibition binds at a separate site from the active site to either the free enzyme or the enzyme-substrate complex.
resembles the non-competitive graph, except that the enzyme-inhibitor-substrate complex has residual enzymatic activity, so some product can still be formed even when inhibitor is bound.
Vmax will be reduced
Km may be increased OR decreased
What is uncompetitive inhibition?
inhibitor binds only to the enzyme-substrate complex, at a separate site from the active site and NOT with the free enzyme.
Vmax and Km are reduced by the SAME amount
(on the straight-line graph, the inhibited enzyme line is parallel but to the left of the uninhibited line, and on the curved-line graph, the inhibited starts off more steeply, but then levels out lower than the uninhibited curve)
Serine Protease Inhibitor is an example of what type of enzyme inhibitor?
Irreversible enzyme inhibitor
proteases typically will attack protein amide bonds. can also attack & break ester bonds.
What is clavulanic acid?
Molecular target: beta-lactamase
MOA: irreversible inhibitor
Disease/symptom: anti-bacterial agent used in combination with penicillin overcoming drug resistance
inhibitor of bacterial beta-lactamase:
beta-lactamase is a serine protease & can hydrolyze beta-lactams, such as penicillin antibiotics (responsible for penicillin-resistant bacteria)
Clavulanic acid is a beta lactam and is preferentially taken up by beta-lactamase & hydrolyzed. during the Clavulanic acid molecule’s cleavage, a Michael acceptor is formed which alkylates a nucleophilic residue on the beta lactamase causing IRREVERSIBLE INHIBITION.
so combining beta lactamase inhibitors like clavulanic acid with penicillin helps combat antibiotic resistance
What are the functions of Acetylcholine in the peripheral and central nervous systems?
Peripheral: activates muscles when it binds to ACh receptors on skeletal muscle fibers and causes muscle contraction. In Cardiac muscle fibers, it binds to muscarinic receptors and INHIBITS contraction.
In autonomic nervous system, ACh is released in the following sites: all pre and post ganglionic parasympathetic neurons, all preganglionic sympathetic neurons, preganglionic sympathetic fibers to suprarenal medulla, modified sympathetic ganglion;
when stimulated by ACh, the suprarenal medulla releases epinephrine and norepinephrine … and more stuff that I don’t think we have to know
Central Nervous System: ACh acts as neuromodulator & effects plasticity, arousal and reward. important role in enhancement of sensory perceptions when we wake up & sustaining attention.
Damage to cholinergic (ACh-producint) system in the brain has been associated with memory deficits associated with Alzheimers disease. ACh also shown to be the most important inducer of REM sleep.
What is muscarine?
Molecular target: Muscarinic receptor
MOA: agonist
Disease/symptom: glaucoma
a natural agonist of the parasympathetic nervous system muscarinic receptors. Mimic of ACh-ase
It comes from the amanita muscaria (a mushroom)
used to treat glaucoma, reducing intraocular pressure
if improperly ingested, it is highly toxic
What is atropine?
Molecular target: Muscarinic receptor
MOA: antagonist
Disease/symptom: used to treat organophosphate poisoning and resuscitation
natural antagonist of the parasympathetic system muscarinic receptors: blocks ACh from binding
comes from Atropa belladonna
used to treat organophosphate poisoning from nerve gas and many other therapeutic effects including resuscitation
What is Physostigmine?
a reversible AChE inhibitor from the African Calabar Bean
Used to treat myasthenia gravis, glaucoma, Alzheimer’s disease and delayed gastric emptying
What is the deal with Sarin gas?
an agent that causes organophosphate poisoning
binds to the esteratic site on AChE
then it goes through an aging process where the second phosphate ester is hydrolyzed and makes the phosphate-ester bond irreversible
you need to get treated right away if you are exposed to war gas, otherwise you are hosed.
What is pralidoxime?
Molecular target: Acetylcholinesterase
MOA: antidote used to remove irreversible organophosphate inhibitors from AChE
Disease/Symptom: organophosphate poisoning
Organophosphate poisoning antidote
War gas is an irreversible inhibitor, but pralidoxime can combat it.
It has an OH group bound to a quaternary nitrogen which makes it a strong nucleophile. Strong enough to pull the phosphate group (bound to AChE) off of the AChE
lots of electron density around the oxygen of the pralidoxime, and little electron density around the phosphate (because it is surrounded by 3 oxygens) of the war gas
What is pyridostigmine bromide?
Molecular target: Acetylcholinesterase
MOA: prophylactic to block or prevent organophosphate poisoning
Disease/symptom: used to prevent organophosphate poisoning but has been linked to Gulf War Syndrome
given to gulf war soldiers as a prophylactic
weak inhibitor of AChE, designed so that it doesn’t enter the CNS
BUT the theory is that under stressful conditions, it does leak into the CNS - may cause Gulf War Syndrome - wreaks havoc on AChE receptors
How does a protein kinase phosphorylate a protein?
the protein has a serine, threonine or tyrosine side chain with an OH group.
ATP and protein kinase phosphorylate the protein at that side chain (put the phosphate group onto the O of the OH. That is the on switch
to turn the protein “off”, protein phosphatase takes off the phosphate group. (regulation of the signaling events)
The signal in causes a protein kinase to phosphorylate (and therefore activate) the enzyme.
role of kinases in cancer
kinases have been shown to play a profound role in cancer tumor progression and initiation. Many are oncogenes (RAS) - overexpression or mutation of RAS can lead to tumor initiation & progression
tyrosine Kinases are targets of anticancer drugs: tyrosine kinase inhibitors - targeting those signaling pathways
What is imatinib?
Molecular Target: BCR-ABL
MOA: Competitive BCR-ABL inhibitor, binds to inactive ABL
Disease/Symptom: used to treat various types of cancer but mainly Leukemia, including: ALL, CEL, CML
What is the Philadelphia Chromosome?
first known fusion enzyme: BCR-ABL fusion protein
ABL part from one chromosome and BCR part from another translocate, overlap and then generate an actual protein with both parts of those enzymes
this fusion protein is hyper-activated in chronic myeloid leukemia
the kinase signaling pathway is the on signal that is never shut off
CML proliferation
lead to the discovery that kinases could be viable targets in cancers and other diseases
What is Dasatinib?
Molecular target: BCR-ABL
MOA: binds to active form of ABL
Disease/symptom: used to treat imatinib resistant leukemia that is Philadelphia chromosome positive
(Sprycel)
a derivative of Imatinib
a tyrosine kinase inhibitor
describe the discovery process of Imatinib
- through HTS, identified a protein kinase C inhibitor fragment. Used fragment based drug design to add a fragment that increased cellular uptake in PKC inhibition (increased activity). BUT determined that it was a “dirty” PKC inhibitor - inhibited many kinds of PKC’s and didn’t inhibit BCR-ABL
- Added another fragment for inhibition of BCR-ABL after more drug design. Still inhibited PKC and other kinases, so had to make it more specific
- Added one methyl group paired to amide increased the BCR-ABL specificity and lost connectivity to PKC
- Drug was further enhanced by adding another functional group which increased water solubility and bioavailability - very important for Imatinib and all kinase inhibitors
How do you treat Imatinib-resistant BCR-ABL?
Dasatinib it inhibits imatinib-resistant BCR-ABL the difference between Imatinib and Dasatinib is the orientation of the activation loop Imatinib binds to inactive ABL Dasatinib binds to active ABL
What is Neostigmine?
Molecular target: Acetylcholinesterase
MOA: reversible inhibitor
disease/symptom: used to treat myasthenia gravis, an autoimmune disease
Nerve gas agents
Sarin, tabun, DFP and VX
Molecular target: Acetylcholinerase
MOA: irreversible inhibitors
Disease/symptom: none but are used in war as chemical war agents and by terrorists
What are the key HIV genes?
Structural genes:
Gag (structural proteins): encodes: matrix, capsid, nucleocapside
pol (enzymes): encodes: protease, reverse transcriptase, integrase
env (surface antigens): encodes: gp 160 consisting of go 120 and gp 41
what does HIV1 protease do?
cuts polypeptide chain (inside mature viral particle) into active proteins
what does integrase do?
incorporates viral DNA into human genome
What are the major targets for HIV drug therapy?
HIV1 protease
Reverse transcriptase
What is the structure of Reverse Transcriptase
ribbon structure
shaped like a hand
palm is the business end - where it does the work with RNA
How does reverse transcriptase bind to deoxy Nucleotide Triphosphate (dNTP)?
the polymerase active site is composed of 3 catalytic carboxylates in the palm subdomain that binds two Mg2+ ions that are required for catalysis. Mg positions the oxygens in the right orientation so that it’s in proximity to the phosphate on the dNTP.
Components of Nucleic Acids
Nitrogen bases: DNA only --> thymine DNA & RNA --> adenine, guanine, cytosine RNA only --> uracil Sugars and phosphate DNA only --> 2-deoxyribose RNA only --> ribose Nucleoside = base + sugar Nucleotide = base + sugar + phosphate
What are the pyrimidine and purine bases?
pyrimidine bases:
cytosine (C) and thymine (T)/ Uracil (U)
Purine bases:
Adenine (A) and Guanine (G)
What are 2 examples of Reverse Transcriptase (RT) inhibitors?
AZT: Nucleoside/nucleotide RT inhibitors (NRTI)
Nevirapine: Non-nucleoside/nucleotide RT inhibitors (Non-NRTI)
what are NRTIs
structurally diverse analogs of the natural substrates of DNA synthesis.
all approved NRTIs lack the 3’-OH and act as chain terminators when incorporated in viral DNA by RT. For NRTIs to be effective against HIV, they have to be taken up by the host cell and then phosphorylated by cellular enzymes to convert them to their active form, the NRTI triphosphates.
efficiency of conversion to active metabolite & stability of NRTIs in presence of catabolic enzymes are important considerations in antiviral therapies, because these factors help determine the concentration of the inhibitor in the bloodstream that is required for the NRTI to be effective
What are NNRTIs
non-competitive inhibitors & do not directly interfere with the binding of either the dNTP or the nucleic acid substrates of RT. Pre-steady state kinetic analysis of single nucleotide addition in the presence of NNRTIs has shown that binding of NNRTI interferes with the chemical step of DNA synthesis
What are some examples of NRTIs
zidovudine lamivudine stavudine didanosine zalcitabine abacavir emtricitabine tenofovir Key point to remember is that the structural activity relationship is all around the sugar.
What are examples of NNRTIs?
Nevirapine Delavirdine Efavirenz Dapivirine Etravirine Rilipivirine No bases or sugars here, just aromatic rings that were found to bind to an allosteric site. Very lipophilic, so lots of lipophilic ring systems and nitrile functionalities
What is the MOA of nucleoside RT inhibitors?
suppress HIV replication by attacking reverse transcriptase
NRTIs are similar in structure to the building blocks that make up DNA. They incorporate themselves into the DNA nucleoside chain being produced by reverse transcriptases, they stop attachment of further nucleosides & so prevent ongoing viral DNA synthesis.
What is the MOA of non-nucleoside reverse transcriptase inhibitors?
Attach to the reverse transcriptase and affect the activity of the enzyme by restricting its mobility and making it unable to function
What is the MOA of AZT?
it is a pro-drug
activated via phosphorylation by host cell, mimicking tri-phosphorylated DNA base
then RT recognizes AZT-PPP & tries to incorporate it into the newly sequenced DNA.
AZT does not contain a hydroxyl functionality so DNA chain termination results.
What are two mechanisms of resistance of HIV to NRT inhibitors
- exclusion: enhanced discrimination at the time the NRTI/TP is incorporated. M184V/I mutation is an example of exclusion mechanism. That mutation selectively reduces incorporation of 3TC and FTC by steric hindrance
- Selective removal of NRTI from end of the viral DNA after it has been incorporated by RT. Excision mechanism; example is AZT resistance caused by set of mutations including M41L, D67N, K70R, L210W, T215F/Y, K219E/Q
What are the most frequently observed resistance mutations in patients treated with approved NNRTIs?
K103N (lysine 103) and Y181C
resistance mutations can occur singly or in combinations
resistance to 1st and 2nd generation NNRTIs can evolve relatively quickly
How can you combat resistance of HIV to NNRT inhibitors?
drug cocktails: NNRT, NRT and protease inhibitors
What does an enzyme catalyst do to activation energy?
lowers it - so increases the rate of reaction
enzyme stabilizes the ES transition state more than it stabilizes ES
how does drug development relate to transition states?
if you design a drug that mimics the transition state of the substrate, then that enzyme will prefer to bind to the drug than to the substrate
How does HIV protease work?
it mediates post-translational modification of core proteins into structural proteins.
HIV genome has regions that are genes (like gag and gag-pol genes) that are translated as polyproteins & form immature viral particles. The precursor protein molecules are cleaved by a viral pol-encoded aspartic proteinase to form the structural proteins of the mature viral particle.
HIV protease also activates RT & plays an important role in release of infectious viral particles.
So inhibiting HIV protease & pol gene is a drug target:
What do HIV protease inhibitors do?
act on HIV protease & prevent post translational processing and budding of immature viral particles from the infected cells.
major breakthrough in treatment of HIV when used in combination with RT inhibitors.
What was the first HIV-1 protease inhibitor?
Saquinavir
What are scissile bonds?
areas along the virus polypeptide where the enzyme recognizes it needs to cut to make active proteins
What is the HIV protease enzymatic mechanism?
Active site triad on the protease (Asp25-Thr26-Gly27) is located in a loop whose structure is stabilized by a network of hydrogen bonds. Carboxylate groups of Asp25 from both chains are nearly coplanar & show close contacts. It is a rigid network due to the “fireman’s grip” interaction in which each Thr26 OG1 accepts a hydrogen bond from the THR26 main-chain NH of the opposing loop.
Drug design of saquinavir
started with a lead structure and then designed off of that using the grow scaffold method (start with fragment & then grow off functional groups)
1. Started with peptidomimetic of a natural substrate of HIV-1 protease. Cbz was added to fill the S2 pocket (Cbz is a standard protecting group) Used “aspartyl warhead” to mimic transition state of peptide substrate. it binds with much greater affinity than the natural substrate would, so it’s a strong competitive inhibitor. Aspartyl warhead is stable & can’t be hydrolyzed like the natural substrate could. Added a t-butyl ester group to the existing proline to strengthen the binding interactiosn to pocket S1’
2. carbon spacer between Cbz group is added with a side chain containing a primary amide group filling pocket S2 - allows the Cbz group to interact with pocket S3. creates significant increase in enzyme inhibition from 6500 nM to 140 nM
3. Cbz group exchanged for a quinoline ring –> increases lipophilic interactions & introduces stronger pi-stacking interaction due to more electron deficient nitrogen ring. - enzyme inhibition goes from 140nM to 23 nM.
4. proline residue was exchanged for a decahydroisoquinoline, occuies the S1’ pocket w/hydrophobic interactions & extends t-butyl ester group into the S2’ pocket. Now enzyme inhibition is 0.4 nM or 400 pM
extremely specific for HIV-1 protease & reduces off target effects
What are some FDA approved HIV-1 protease inhibitors (transition state analogs)?
Amprenavir Saquinavir Indinavir Lopinavir Ritonavir Nelfinavir all of these are peptidomimetics & used along with reverse transcriptase inhibitors
What is Darunavir?
second generation HIV protease inhibitor.
designed the drug better (than saquinovir), increase interactions with the inhibitor and overcome drug resistance (mutations that led to minimal structural changes in the active site of HPI).
Has many characteristics of saquinovir with isosteric replacement
What is the basic timeline of bacteria/antibiotic discovery?
1670’s bacteria discovered by Leeuwenhoek
1859 - Pasteur demonstrated that microorganisms grow rather than spontaneously generate (germ theory of disease)
1905 - Koch - proved germ theory
1940’s - 1st mass produced antibiotic - penicillin- used during WWII
What kind of products are antibiotics?
natural
Fleming discovered penicillin when he noticed clear circles around mold on a petri dish (the mold was penecillium)
Explain selective toxicity
common processes mediated by different proteins: because of evolutionary distance between bacterial cells and eukaryotic cells, so a compound that inhibits a biosynthetic bacterial enzyme has little or no effect on eukaryotic counterpart
cell wall vs. plasma membrane: bacterial cells have some structures that are unique, so we can target those things - like components of bacterial cell wall
How does bacterial resistance arise?
bacterial mutations accumulate rapidly
antibiotics place strong selective pressure on bacterial populations driving evolution of resistant strains
-exposure to low antibiotic blood concentration gives bacterial population time to accumulate sufficient mutations to develop resistance
How do bacteria exchange genetic information?
Transformation: fragments of DNA from dead bacteria are picked up by recipient
Transduction: viruses (bacteriophage) pick up a piece of genome accidentally and insert it into recipient upon infection
Conjugation: physical bridge formed between cytoplasms. F plasmid (fertility factor) is expressed by donor, it is copied & copy is transferred to recipient. THIS is the most common form of exchange
What are the mechanisms of resistance
- Bacterium may have altered the target such that antibiotic binding affinity is vastly reduced
- bacterium may have eliminated the target altogether
- bacterium may either restrict access or actively pump the antibiotic out of the cell
- bacterium may express an enzyme that inactivates the antibiotic
- bacterium may express a biofilm that restricts access
- bacterium may have entered a state of quiescence.
What are the beta-lactam ring antibiotics?
Inhibit cell wall
Penicillins, cephalosporins, carbapenems, monobactams
all share Beta-lactam ring structure which is essential to the function of these compounds: beta lactam ring is highly reactive due to the geometry of 4 atoms in the ring (looks like a square)
Describe the structure of gram positive bacterial cell wall
simpler structure of the two (gram positive & gram negative) outermost layer is carbohydrates and proteins, below that is cross-linked peptidoglycans (sugar chains with amino acids that are in D conformation (not L)) arranged in layers that are cross-linked laterally and above and below (this makes the rigid cell wall). Under that is lipid bilayer containing proteins. Some of those proteins are responsible for constructing the cell wall - they are called PBPs (penicillin binding proteins) b/c they serve as targets for this class of antibiotic. There are 7 different PBPs & different penicillins have different patterns of binding to subsets of these proteins
Describe the structure of a gram negative bacterial cell wall
outer lipid membrane that is distinct & different from inner lipid membrane. It contains porins which function to exclude certain molecules while allowing others to pass. Porins make entry of antibiotics more difficult. Other proteins induce septic shock in the host & may supply antigenic determinants which can be used by the immune system.
below the lipid membrane is a peptidoglycan layer (thinner than in gram positive). This region is called the periplasmic space.
Below this is the inner plasma membrane that contains PBPs along with other proteins that are involved in the transport of nutrients and waste
What do penicillin binding proteins do?
build and repair the bacterial cell wall
7 different proteins - each is an enzyme that constructs some aspect of the peptidoglycan layer
because there are multiple PBPs, different penicillins are going to bind differently & inhibit different proteins; they are going to work differently in different bacteria, because each bacteria has a different set of PBPs.
What does PBP-1 do?
it is a transamidase that crosslinks peptidoglycan strands
accepts a terminal D-ala-D-ala peptide into its active site (that is what is going to cross link)
certain penicillins take the place of D-ala-D-ala.
When PBP-1 tries to convert it, the Beta-lactam ring breaks & attaches permanently to the enzyme, inactivating it. (covalent bond)
Why are there so many beta-lactam antibiotics?
each beta lactam antibiotic has a different (but overlapping) spectrum of activity because it has different abilities to inactivate different PBPs.
amino acid sequences are different in the various PBPs, so any one specific antibiotic will bind with different affinities
What is the major form of bacterial resistance to beta-lactam antibiotics?
ability of the bacteria to express an enzyme that cleaves the beta-lactam ring (beta-lactamases)
many different beta-lactamases are produced by different bacteria, and different penicillins have various sensitivities to these inactivating enzymes.
–> Different species of bacteria are differently resistant to certain penicillins
what is the basic structure of penicillin?
Pentagonal ring attached to a beta-lactam ring.
Carbon 6 is on the beta-lactam ring, the side chain on carbon 6 determines the specific type of penicillin
What were the first penicillins?
fermentation derived penicillins
these were secreted by the penicillium fungus. The side chain was derived from substances in the media, so it was possible to alter the media to create Penicillin G (Benzylpenicillin) or Penicillin V (Phenoxymethylpenicillin)
They work against most non-resistant gram positive bacteria, cheap, relatively non-toxic (except for allergies)
Penicillin V is more acid stable than G, so it survives the stomach better - better for oral administration
What is an example of a parenteral penicillin?
Methicillin
Semi-synthetic penicillinase-resistant parenteral penicillin
could remove the side chain completely by leaving out that constituent of the media where penicillin was grown. Parent molecule was harvested, and synthetic side chains were added at C6.
Methicillin is not used today due to drug resistance
What are examples of semi-synthetic penicillinase-resistance oral penicillins?
Oxacillin (Bactocil)
Cloxacillin (Cloxapen)
Dicloxacillin (Dycill, Pathcil)
What are examples of penicillinase-sensitive, broad-spectrum oral penicillins?
Amoxicillin
Ampicillin
these are effective against some gram negative as well as gram positive bacteria
What are examples of semi-synthetic penicillinase-sensitive, broad spectrum, parenteral penicillins?
Carbenicillin (Geocillin)
Ticarcillin (Ticar)
Mezlocillin (Mezlin)
Piperacillin (Pipracil)
What is Augmentin?
Amoxicillin (broad spectrum orally active penicillin which is sensitive to beta-lactamases) and Clavulanic acid (beta lactam molecule which is weak by itself as an antibiotic, but great inhibitor of beta-lactamases.
successful strategy: combine an antibiotic with an inhibitor of one or more resistance genes.
Why so many penicillin allergies?
6-8% of US population is allergic to penicillins
one of the major reasons is that penicillins can form haptens - a small molecule covalently attached to a protein which creates a potent epitope for an immune response.
the beta-lactam ring can be hydrolyzed in the liver leading to protein conjugation.
What are Cephalosporins?
Beta-lactam molecules
original (natural one) was not very potent, but quite resistant to beta-lactamases.
synthetic chemistry has generated 1000’s of different molecules - there are several places we can add groups (unlike penicillins where it’s just the C6) - allow us to maintain activity & alter function
can be broad spectrum and are being used against some very dangerous pathogens - hospital acquired infections are one example
Give examples of 1st through 3rd generation cephalosporins
1st generation: Cephalexin
3rd generation: Cefotaxime
4th generation: Cefepime (he didn’t give an example of 2nd)
What are classes of synthetic antimicrobials?
And what are their MOAs
Sulfonamides Trimethoprim Quinolones Nitroheteroaromatic compounds Inhibit various aspects of nucleic acid (DNA and RNA) biosynthesis and function.
Sulfonamides
Examples: Sulfamethoxazole, Sulfadiazine
Inhibit dihydropteroate synthase (an intermediate in DNA synthesis)
These used to be broad spectrum, but resistance has vastly decreased their use
resistance involves mutations in the dihydropteroate synthase enzyme
subsequent mutations allow folate to be harvested through other pathways.
Examples of Quinolones, how they work, and mechanisms of resistance
Examples: Ciprofloxacin, levofloxacin
Inhibit bacterial DNA gyrase and topoisomerase IV. This inhibits gene transcription (rather than inhibiting DNA synthesis, we are inhibiting DNA function)
Resistance mechanisms:
-mutations in DNA gyrase
-inhibition of drug entry (gram negative bacteria)
-increased drug efflux (gram negative bacteria)
