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(1)محمد نورالدين محمود كيمياء دوائية
Drug targets • Drug targets are usually functional macromolecules
(mainly proteins but can be others like DNA, etc.) involved in specific biological action.
• Drug targets can be referred as receptors (Targets=Receptors).
• The interaction of drug molecule with those targets will produce biological response.
• Drugs usually disturb the normal function of the targets biological effect.
• For a drug to selectively disturb the function of a particular target, it should bind selectively to the target. Nothing is better than mimicking the specific substrate of that target.
• The substrate and the drug bind to specific site on the macromolecule known as the ‘binding site’.
• Most drugs disturb the normal biochemical reactions. معظم االدوية هي عبارة عن مواد معطلة للتفاعالت العادية داخل الجسم
Specific receptors
Hopkins, A.L. and Groom, C.R., 2002. The druggable genome. Nature reviews Drug discovery, 1(9), pp.727-730.
Hopkins, A.L. and Groom, C.R., 2002. The druggable genome. Nature reviews Drug discovery, 1(9), pp.727-730.
• Drug targets are macromolecules of various structures, functions and intracellular locations.
• The drug targets can be classified mainly into:
1. Enzymes e.g. angiotensinogen converting enzyme
2. G-protein coupled receptors e.g. β-adrenergic receptors
3. Ion channels e.g. calcium channels
4. Nuclear receptors e.g. insulin receptor
Intermolecular interaction between drug and target
• The strength of drug-target interaction is measured as energy (Kcal/Mol). Which means the amount of energy required to separate them away from each other.
• Some drug-target interactions are so strong, and are due to the formation of covalent bond (200-400 Kj/Mol). Such drugs are long acting drugs
• Some drug-target interactions are weak, and are due to non-covalent bonds (H-bonds, electrostatic, ionic, van der Waals, dipole-dipole and hydrophobic interactions). Such drugs are short acting drugs.
• The energy of drug-target interaction determines the time period the drug occupies target binding site (which can be measured by Kd)
• The drug molecule composed from carbon skeleton (which give the steric shape) and functional groups (binding groups) which specifically binds to receptor.
Cellular location of receptor molecules
1. Cell membrane
2. Cytoplasm
3. Nuclear membrane
4. Nucleus
Ligand molecules
• Not all small drug molecules act through specific receptors.
• Some small drug molecules interacts non-specifically with lipopolysaccharides, carbohydrates and DNA (unlimited receptors)
For example: some group of compound used as narcotics or anaesthetics, the pharmacological effect is mainly related to physical rather than chemical properties. In other word, Those group of compounds
1. Contain diverse chemical groups
2. Their pharmacological effect is attained rapidly and disappear rapidly when the supply is removed (i.e. equilibrium is exist between the external phase and biophase)
• Other small drug molecules interacts specifically to protein (most common) or DNA/RNA (less common) (limited receptors). Why?
For example: most the available drugs. Those group of compounds
1. Contain specific scaffold (molecular frame or molecular backbone) in common to drugs act on same receptor
2. Their pharmacological effect is attained rapidly and disappear slowly when the supply is removed (i.e. equilibrium is exist between the free and receptor bound form)
Specific and non-specific binding of ligands
receptor
receptor
Drug molecule act through
specific receptor
Drug molecule act through non-specific receptor
Affects membrane solubility Like some anesthetics and antifungal agents
Binds to DNA Like some anticancer agents
Binds to specific receptor Like enzyme (agonists/antagonists) Cell-membrane receptors (agonists/antagonists) Nuclear receptor (agonists/antagonists)
Cell
Binds to proteins Like free radicals and some poisons
Specific and non-specific binding of ligands • On the basis of the mode of action, drugs are divided into two categories
Ligands act through non-specific binding Ligands act through specific binding
1 Number of receptors is unlimited (very high) Number of receptors is limited (low)
1 Their biological action is directly related to affinity to non-specific receptor (measured by K), follow 1st order kinetics, cannot get saturated and competed
𝐴𝑐𝑡𝑖𝑣𝑖𝑡𝑦 = 𝐾𝐶
Their biological action is directly related to affinity to receptor (measured by Kd) and follow 2nd order kinetics, can be saturated and competed
𝐴𝑐𝑡𝑖𝑣𝑡𝑖𝑦 =𝑉𝑚𝑎𝑥𝐶
𝐾𝑑 + 𝐶
2 High doses are needed for biological activities They are effective in low concentrations
3 Chemical structures are different, but they produce similar biological responses (drug design is easy)
They have some structural characteristics in common to produce the biological Response (drug design is difficult)
4 Slight modifications in their chemical structure do not result in pronounced changes in biological action
Slight modifications in their chemical structure may result in substantial changes in biological activity
5 More toxic Less toxic
+ 𝐾𝑜𝑛
𝐾𝑜𝑓𝑓 +
𝐾𝑜𝑛
𝐾𝑜𝑓𝑓
•Differences between structurally nonspecific drugs and structurally specific drugs
1. Drugs act through non-specific receptors 2. Drugs act through specific receptors
Example of drugs acting through non-specific receptors
• Amphotericin B and Miltefosin are example of drugs act by non-specific binding
• Drugs have less similar structures
• Both drugs used as antifungal agents.
• Both drugs disturb the phospholipid membrane integrity by acting as surface-active agents.
• Toxic when used systematically
Miltefosin
CELLMEMBRANE
TUNNEL
HO
HO
HO
HO
HO
HO
HO
HO2C CO2H
Sugar
OH OH
Sugar
HO
HO
HO
HO
HO
HO
HO
OH
OH
OH
OH
OH
OH
OH
Sugar
OH OH
Sugar
HO2C CO2H
OH
OH
OH
OH
OH
OH
OH
Example of drugs acting through non-specific receptors (Cont.)
• Action of amphotericin B (antifungal agent)
• Builds tunnels through membrane and drains cell
Hydrophobic region
Hydrophilic Hydrophilic
Hydrophilic
OOH
HO
OHHOOC
OH
O
Me
OH
OH
Me
OH O OH
Me
O
O
HONH2
HO
Me
H
Polar tunnel formed
Escape route for ions
Example of drugs acting through non-specific receptors (Cont.)
Na+
ch
ann
el
• Some anesthetic agents are also belong to the group of non-specific acting drugs.Substances like alkanes, alkenes, alkynes, ketones, amides, chlorinated hydro-carbons, ethers and alcohols display narcotic activity which is directly proportional to the partition coefficient of each individual substances.
• the interaction of the anesthetic molecules with a hydrophobic portion of the nerve membrane caused a distortion of the nerve membrane near the channels that conducted Na+, those that mediated the fast action potentials and neuronal cell firing.
Example of drugs acting through non-specific receptors (Cont.)
PO4- PO4
-
PO4- PO4
-
PO4- PO4
-
+NR4
• Intercalating agents are group of anticancer agents which act by non-specific binding .
• The intercalating agents have no specific structures, except having planner aromatic system and a polar amino group
Case study for compounds act through non-specific receptors:
• The correlation between lipid solubility and anesthesia measured by tadpole motility.
Compound Partition coefficient (n-Octanol/Water)
Required cnoc. to immobilize tadpole
Calcul. Depressant Conc in cellular lipids
1 Thymol 0.000047 950 من الزعتر moles 0.045
2 Valeramide-OM 0.03 0.07 mol2 0.021
3 2-nitro aniline 14 0025 moles 0.035
Thymol Valeramide-OM 2-nitro aniline
Specific drug receptors • The drug can bind to specific receptor (target) to form complex.
• The drug-receptor complex will lead the receptor function to be affected in different ways depending on type of receptor and (ligand):
• The specific drug receptors can be classified into:
A) Machine receptors: like all enzymes 1. Active (Substrate)
2. Inactive (Inhibitor)
B) Switch receptors: like transmembranal proteins (sensors, ion channels) and enzymes contain allosteric switches 1. OFF (Inhibitor / antagonist)
2. ON (Potentiator / agonist)
3. OFF with partial ON (partial antagonist)
4. ON with partial OFF (partial agonist)
5. Partial OFF and cannot be completely OFF by antagonist (inverse antagonist)
6. Partial ON and cannot be completely ON by agonist (inverse agonist)
receptor
Drug
+ 𝐾𝑜𝑛
𝐾𝑜𝑓𝑓
Pharmacological effect
OFF (antagonist)
ON (agonist)
Partial ON (Partial agonist)
Partial OFF (Partial antagonist)
Partial OFF difficult to be completely OFF
(Inverse antagonist)
Partial ON difficult to be completely ON
(Inverse agonist)
Enzyme
Substrate
Product Drug
Substrate
Inhibitor Drug
Switch
Machine
Cell membrane
Like GPCR e.g. adrenergic receptors, etc.
Like most enzymes e.g. acetylcholine estrase, peptidase, etc.
Self controlled Machine
Like enzymes with allosteric site. e.g.
Diagram represent most known specific receptors
• Even switch receptors are directly or indirectly regulates enzymatic reactions.
• Therefore, enzymes are considered (directly or indirectly) the most important type of specific drug receptors.
• Each enzyme catalyze specific set of biochemical reactions, therefore, inhibition of specific enzyme lead to specific set of pharmacological effects.
Reversible interaction
+
+
S E ES
ES++ E P
You can view energy in different ways
• This is how we can correlate interaction energy with Kd
∆𝑯 − 𝑻∆𝑺 = ∆𝑮 = −𝑹𝑻 𝒍𝒏𝑲𝒅
-ve for spontaneous rxn +ve for nonspontaneous rxn Zero at equilibrium (i.e. at Kd=1) Path independent (depend on starting and
end states) Gives information on rxn spontaneousity Gives NO information on rxn rate
The change in energy مقدار التغير في الطاقة
−𝑹𝑻 𝒍𝒏𝑲𝒅
𝐾𝑜𝑛
𝐾𝑜𝑓𝑓 +
• Therefore, enzymes are considered the most important type of drug receptors.
• Each enzyme catalyze specific set of biochemical reactions, therefore, inhibition of specific enzyme lead to specific set of pharmacological effects.
Reversible interaction
+
+
S E ES
ES++ E P
Free energy diagram for the reaction pathway of a chemical reaction, and the same reaction catalyzed by an enzyme. Note the significant reduction in activation energy (the vertical distance between the reactant state and the transition state) achieved by the enzyme-catalyzed reaction
Principles of enzyme function
• 𝐾𝑑 =𝐾𝑜𝑓𝑓
𝐾𝑜𝑛
• ∆𝐺 = −𝑅𝑇 ln 𝐾𝑑
• ∆𝐺𝐸𝑆 = −𝑅𝑇 ln 𝐾𝑠 (Energy to form ES)
• ∆𝐺𝐾𝑐𝑎𝑡 = −𝑅𝑇 ln 𝐾𝑐𝑎𝑡 − − 𝑅𝑇 ln𝐾𝐵𝑇
ℎ
• ∆𝐺𝐸𝑆++ = −𝑅𝑇 ln𝐾𝑐𝑎𝑡
𝐾𝑠− − 𝑅𝑇 ln
𝐾𝐵𝑇
ℎ
−𝑅𝑇 ln 𝐾𝑐𝑎𝑡 E + S ES ES++ EP E + P
𝐾𝑠 𝐾𝑐𝑎𝑡 ~1 𝐾𝑝
Drive of random motion
Principles of enzyme function
• The reason for the slow rates of most reactions involving organic substances is the high activation energy that the reacting molecules have to reach before they can react.
• A catalyst creates a new pathway for the reaction. When all of the transition states arising have a lower activation energy than that of the uncatalyzed reaction, the reaction will proceed more rapidly along the alternative pathway, even when the number of intermediates is greater.
• Catalysts—including enzymes—are in principle not capable of altering the equilibrium state of the catalyzed reaction.
• The often-heard statement that “a catalyst reduces the activation energy of a reaction” is not strictly correct, since a completely different reaction takes place in the presence of a catalyst than in uncatalyzed conditions.
Koolman, Jan, et al. Color atlas of biochemistry. Vol. 2. Stuttgart: Thieme, 2005.
How uncatalyzed reactions proceed • The reaction A + B C + D is used as an
example. In solution, reactants A and B are surrounded by a shell of water molecules (the hydration shell), and they move in random directions due to thermal agitation. They can only react with each other if they collide in a favorable orientation. This is not very probable, and therefore only occurs rarely.
• Before conversion into the products C + D, the collision complex A-B has to pass through a transition state, the formation of which usually requires a large amount of activation energy, Ea. Since only a few A–B complexes can produce this amount of energy, a productive transition state arises even less often than a collision complex.
• In solution, a large proportion of the activation energy is required for the removal of the hydration shells between A and B. However, charge displacements and other chemical processes within the reactants also play a role.
• As a result of these limitations, conversion only happens occasionally in the absence of a catalyst, and the reaction rate v is low, evenwhen the reaction is thermodynamically possible—i. e., when ΔG < 0.
• Enzymes are able to bind the reactants (their substrates) specifically at the active center. In the process, the substrates are oriented in relation to each other in such a way that they take on the optimal orientation for the formation of the transition state (1–3).
• The proximity and orientation of the substrates therefore strongly increase the likelihood that productive A–B complexes will arise. In addition, binding of the substrates results in removal of their hydration shells. As a result of the exclusion of water, very different conditions apply in the active center of the enzyme during catalysis than in solution (3–5).
• A third important factor is the stabilization of the transition state as a result of interactions between the amino acid residues of the protein and the substrate (4). This further reduces the activation energy needed to create the transition state. Many enzymes also take up groups from the substrates or transfer them to the substrates during catalysis..
• Proton transfers are particularly common. This acid–base catalysis by enzymes is much more effective than the exchange of protons between acids and bases in solution. In many cases, chemical groups are temporarily bound covalently to the amino acid residues of the enzyme or to coenzymes during the catalytic cycle. This effect is referred to as covalent catalysis.
How catalyzed reactions proceed
How enzyme catalyzes the reaction • Although it is difficult to provide
quantitative estimates of the contributions made by individual catalytic effects, it is now thought that the enzyme’s stabilization of the transition state is the most important factor.
• It is not tight binding of the substrate that is important, therefore—this would increase the activation energy required by the reaction, rather than reducing it—but rather the binding of the transition state.
• This conclusion is supported by the very high affinity of many enzymes for analogues of the transition state. A simple mechanical analogy may help clarify this (right). To transfer the metal balls (the reactants) from location EA (the substrate state) via the higher-energy transition state to EP (the product state), the magnet (the catalyst) has to be orientated in such a way that its attractive force acts on the transition state (bottom) rather than on EA (top).
What is • Enzymes are proteins that function as catalyst for chemical reactions.
• Chemical reactions catalyzed by enzymes are called “biochemical reactions”.
• Enzymes harbor a site which can bind the reactant (substrate) and convert it into product.
• Enzymes do: - Accelerate rate of chemical reactions
- Act on specific molecules of substrates and products
- Induce strains and perturbations that convert the substrate into transition state structure.
- Bind to substrate in thermodynamically favorable way
- Do catalyze reaction by regio- and stereo- (enatiomerically) selective way
• The enzyme active site: - Is small in size
- Has 3D shape
- Interacts with substrates by initial non-covalent interactions
- Present in cleft or cavity
How enzyme catalyzes the reaction (Cont.)
• Enzyme catalyzes reaction by:
1. Binding substrate molecule through reversible non-covalnet interactions
2. Shielding substrate molecules from bulk solvent and creating a localized dielectric environment that helps reduce the activation barrier to reaction
3. Binding substrate(s) in specific orientation that aligns molecular orbitals on the substrate molecule(s) and reactive groups within the enzyme active site for optimal bond distortion (orbital steering) as required by the chemical transformation of catalysis.
4. Stabilize the steered molecular orbitals
5. May temporarily binds to a chemical group of one of the substrates before transferring it to the other.
Common features for enzyme active site • Some of the salient features of active site structure that relate to enzyme catalysis and ligand (e.g.,
inhibitor) interactions include:
1. The active site of an enzyme is small relative to the total volume of the enzyme.
2. The active site is three-dimensional—that is, amino acids and cofactors in the active site are held in a precise arrangement with respect to one another and with respect to the structure of the substrate molecule. This active site three-dimensional structure is formed as a result of the overall tertiary structure of the protein.
3. In most cases the initial interactions between the enzyme and the substrate molecule (i.e., the initial binding event) are noncovalent, making use of hydrogen bonding, electrostatic, hydrophobic interactions, and van der Waals forces to effect binding.
4. The active site of enzymes usually are located in clefts and crevices in the protein. This design effectively excludes bulk solvent (water), which would otherwise reduce the catalytic activity of the enzyme. In other words, the substrate molecule is desolvated upon binding, and shielded from bulk solvent in the enzyme active site. Solvation by water is replaced by specific interactions with the protein.
5. The specificity of substrate utilization depends on the well-defined arrangement of atoms in the enzyme active site that in some way complements the structure of the substrate molecule.
• Two types of amino acids available inside enzyme active site:
• Catalytic amino acids: directly or indirectly participate in enzyme-substrate interactions
• Non-catalytic amino acids:
• Complete the construction of active site pocket
• Help shaping tunnels and opening to active site, especially when the pocket is deep inside.
• Might play role in binding (anchoring) substrate to bring it close to catalytic amino acids.
• Evacuate the site from water ↓dielectric constant ↑interaction
Inhibitor interaction MAY or MAY NOT be similar to substrate interaction
Interactions of the dihydrofolate reductase active site with the inhibitor methotrexate (left) and the substrate dihydrofolate (right) in similar manner.
Methotrexate (inhibitor)
Dihydrofolate (Substrate)
How to inhibit truck movement
• To inhibit a truck movement, you can either: - Destroy the truck
- Destroy the engine
- Remove the spark plug
- Cover the spark plug with grease √
• According to easiest method to stop a truck, there is no need to fully occupy the enzyme active site in order to stop enzyme function. You can simply cover part of the active site by a compound.
• Effective small molecule inhibitors of ACE, such as the antihypertensive drugs captopril and enalapril, function by chelating the critical zinc atom and thus disrupt a critical catalytic component of the enzyme’s active site without the need to fill the entire volume of the angiotensin I binding site.
Angiotensin I (Big substrate)
Captopril (small inhibitor)
Degree of specificity • Although they are classified as specific receptors, the degree
of specificity is variable.
• According to degree of specificity to substrates, enzymes can be classified into:
1. Very specific: in which only specific substrate can fit the active site. E.g. carboxyestrase, COMT, Acetylcholine estrase.
2. Not very specific (Broad): in which a set of specific substrates can fit the active site. E.g. peptidases, cytochrome P450, glutathione-S-transferase, and other xenobiotic metabolizing enzymes.
• It is the shape and amino acid composition of the active site which provides the specificity.
• Frequently less specific enzymes have wide active site.
Acetylcholine estrase binds acetylcholine (2HA4)
Glutathione-S-transferase binds GS-CDNB (1XWK)
Specificity parameters
1. Regio-specificity
• Enzymes are regio-specific i.e. catalyse reaction on specific group at specific position even if another identical group is available elsewhere.
• Example:
• Catecholamine-O-Methyl Transferase (COMT): only methylates hydroxyl group that is meta to amino ethylene group
COMT
SAM
Specificity parameters (Cont.)
2. Stereo-specificity
• Enzymes are stereo-specific i.e. bind to specific isomer or enantiomer of substrate (as well as inhibitor).
• Therefore, only single isomer of drug is usually active.
• Examples: • R isomer of Adrenaline is much more active than S
• R isomer of Salbutamol is much more active than S
• S-methacoline is more active than R-methacoline
• S-ibuprofen is more active than R-ibuprofen
Specificity parameters (Cont.)
• For example, the levorotatory form of epinephrine is one of the principal hormones secreted by the adrenal medulla.
• When synthetic epinephrine is given to a patient, the (-) form has the same stimulating effect as the natural hormone. The form (+) lacks this effect and is mildly toxic
Cla
ssif
icat
ion
of
amin
o a
cid
s
Types of enzyme inhibitors
• Enzyme can be inhibited by three types of molecules
1. Competitive inhibitors:: Molecules bind at the active site. Usually the molecules are structural analogues to the substrate and can do compete the substrate at the active site
2. Uncompetitive inhibitors: Molecules bind at the allosteric (switch) site. Usually the molecules are not similar to the substrate and do not compete the substrate at the active site.
3. Non-competitive inhibitors: Molecules bind at both active and allosteric sites. Usually the molecules show partial competition for the substrate at the active site.
• For an enzyme inhibitor to be used as drug it should:
1. The enzyme catalyases a biochemical reaction which lead to disease
2. The enzyme binding pocket has less cross-similarity to other enzymes, thus can be selectively inhibited by drug (𝐾𝑖 < 𝐾𝑠𝑖𝑑𝑒).
Example of enzyme inhibitors used as drugs • Enzyme inhibitor
1. Aminotransferase - Function: deactivates GABA (resting neurotransmitter) - Inhibition: ↑ GABA anticonvulsant effect
2. Xanthine oxidase - function: oxidize xanthine to uric acid (accumulated in joints) - Inhibition: ↓uric acid production treatment of gout
3. Beta-lactamase - function: destroy beta-lactam of penicillin (provide bacterial resistance to penicillin) - Inhibition: ↓ destruction of penicillin improve the spectrum of penicillin
4. Dihydropteroate synthase and folate reductase - function: both enzymes act in the same pathway for synthesis of folic acid in bacterial cell - Inhibition: ↓ biosynthesis of folic acid stop replication of bacterial cell - This is an example of “synergism” in which if two types of inhibitors are used to inhibit two different
enzymes involved in a single pathway. The benefit of synergism is higher activity with lower doses of each inhibitor
• Some of the switch receptors are very rapid (e.g. those involved in synaptic transmission operating within milliseconds), and others very slow (e.g. hormone receptors operate after hours and days.
• Switch receptors can be classified into: 1. Ligand-gated ion channels
2. G-protein-coupled receptors
3. Kinase-linked receptors
4. Nuclear receptors
Cell membrane
2. Switch receptors
Enzyme
1. Ligand-binding domain Extracellular to allow easy access for ligands. Strong affinity for specific ligands - allows different ligands that bind to the same receptor to evoke particular cellular responses. 2. Transmembrane domain Contains a series of hydrophobic amino acids. Tethers the receptor to the cell membrane. 3. Cytosolic "active" enzyme domain Either intrinsic to the receptor or tightly bound via the cytosolic domain. The majority are kinases; they phosphorylate specific threonine, serine, and tyrosine amino acid residues (THR,S,TY = THIRSTY)
Switch
Components of switch receptors
Signal transduction between switch and enzyme
• Such processes take place in as little as a millisecond or as long as a few seconds. Slower processes are rarely referred to as signal transduction
• Activation of switch enables:
1. Extracellular molecules to affect cellular function without entering the intracellular environment.
2. Different intracellular signals to affect the signal of switch by facilitating or inhibiting the activation of regulatory enzymatic proteins (connected to switch) via common or opposing metabolic pathways.
3. Augmentation of signal strength by the activation of enzymes and the production of second messengers (e.g., cAMP, diacylglycerol [DAG], and IP3). Thus an initially weak signal can be amplified many times, and its duration prolonged, to produce a robust cellular response.
Types of switch receptors
1. Ligand-gated ion channels:
• The ligand-gated ion channels are also known as ionotropic receptors.
• These are membrane proteins with a similar structure to other ion channels, but incorporating a ligand-binding site (switch receptor), usually in an extracellular domain.
• Typically, these are the receptors on which fast neurotransmitters act.
• Examples: nicotinic acetylcholine receptor, GABA receptor, and glutamate receptor of N-methyl-D-aspartic acid (NMDA),
• Textbook of Medicinal Chemistry Vol I 1st Edition Authors: V Alagarsamy
Types of switch receptors (Cont.)
2. G-protein-coupled receptors (GPCR)
• GPCR is also called metabotropic receptors or seven-trans membrane spanning receptors that act through a second messenger, which elicits an action.
• Second messengers usually are cyclic adenosine monophosphate (cAMP) and inositol trisphosphate (IP3) produced by cytoplasmic enzymes linked to the receptor.
• Examples: muscarinic acetylcholine receptors, beta adrenergic receptors, serotonin receptors, opioid receptors and glucagon receptors.
• Textbook of Medicinal Chemistry Vol I 1st Edition Authors: V Alagarsamy
Types of switch receptors (Cont.)
3. Kinase-linked or enzyme-linked receptors:
• These constitute extracellular ligand-binding domain that is
• linked to an intracellular domain by a single transmembrane helix. In many cases, the intracellular domain is enzymatic in nature. Examples include receptors for insulin and various cytokines and growth factors.
• Textbook of Medicinal Chemistry Vol I 1st Edition Authors: V Alagarsamy
When the ligand binds a protein kinase-associated receptors, the kinase activity is stimulated and a cascade of phosphorylation transmits the signal
Types of switch receptors (Cont.)
4. Nuclear receptors:
• The nuclear receptors regulate the gene transcriptions, are located in the cytosol, and migrate to the nuclear compartment when a ligand is present.
• The receptor protein is inherently capable of binding to specific genes. These include the receptors of glucocorticoids and thyroid hormone.
Enzymes and switches inhibitors
• As mentioned previously, drugs may bind to switch or enzyme (mainly through reversible non-covalent interaction).
• Drugs affecting switch function are ranged from antagonist, partial antagonist, inverse antagonist, inverse agonist, partial agonist, and agonist)
• Drugs acting on enzyme are substrates or inhibitors.
• What will be the case if enzyme in cytoplasm carries its switch?
• Drugs acting on enzyme that has switch (allosteric site) are range from competitive inhibitors (acting on active site) or uncompetitive inhibitor (acting on allosteric site), or mixed mode inhibitor (acting on both sites).
• Mixed mode inhibitors are called Non-competitive inhibitors
Enzyme
Switch
Competitive
Non-competitive
Uncompetitive
