Modes of Enzyme Inhibition and Regulation PDF

ENZYME INHIBITION ENZYME INHIBITOR – is a substance that slows or stops the normal catalytic function of an enzyme by binding...

ENZYME INHIBITION ENZYME INHIBITOR – is a substance that slows or stops the normal catalytic function of an enzyme by binding to it. Modes of Enzyme Inhibition 1 2 REVERSIBLE COMPETITIVE ENZYME INHIBITION INHIBITOR Type of inhibition to which a molecule that sufficiently resembles an enzyme substrate in shape and charge distribution – that it can compete with the substrate for occupancy in the enzyme’s active site. 3 4 REVERSIBLE COMPETITIVE REVERSIBLE COMPETITIVE INHIBITOR INHIBITOR 5 6 1  REVERSIBLE COMPETITIVE REVERSIBLE COMPETITIVE INHIBITOR INHIBITOR If the inhibitor concentration is greater than the substrate concentration – inhibitor effect dominates. Increasing the concentration of substrate will reverse the effect. 7 8 REVERSIBLE COMPETITIVE REVERSIBLE NONCOMPETITIVE INHIBITOR INHIBITOR EXAMPLES: Is a process by which a molecule that Treatment of methanol poisoning by decreases enzyme activity by binding to giving ethanol intravenously. a site of an enzyme that is not the Action of antihistamine drugs that active site. competes with histidine for reaction with histidine decarboxylase. 9 10 REVERSIBLE NONCOMPETITIVE INHIBITOR 11 12 2  REVERSIBLE NONCOMPETITIVE REVERSIBLE NONCOMPETITIVE INHIBITOR INHIBITOR The substrate can still occupy the active Increasing the concentration of site but the inhibitor’s presence can substrate – no effect. change the structure of the enzyme – Lowering the concentration of the sufficiently prevent the catalytic groups inhibitor – may free up many enzymes from performing catalytic function. to return to normal activity. 13 14 REVERSIBLE NONCOMPETITIVE IRREVERSIBLE INHIBITOR INHIBITOR EXAMPLE: Is a process in which a molecule that Inhibitors such as Pb2+, Ag+, and Hg2+ inactivates enzymes by forming a can bind to a site that are rich in –SH strong covalent bond to an amino acid groups that results in disruption of side – chain group at the enzyme’s secondary and tertiary enzyme active site. structure. 15 16 IRREVERSIBLE INHIBITOR IRREVERSIBLE INHIBITOR The enzyme is permanently EXAMPLES: deactivated. How antibiotics work. Action of chemical warfare agents (nerve gases). Organophospahte insecticide (DDT) mode of action. 17 18 3  WHY NEED TO REGULATE ENZYME PROCESSES? Main reason is to minimize the process of energy-wasting. Any increased substrate-to-product output due to too much enzyme concentration will lead also to increased energy utilization. Regulation of Enzyme Activity 19 20 WHY NEED TO REGULATE ENZYME REGULATION MECHANISM PROCESSES? That is why there are several “turn off” 3 general mechanisms: and “turn on” mechanisms to regulate Feedback control – associated with and avoid energy-wasting scenarios. allosteric enzymes Proteolytic enzymes and zymogens Covalent modification 21 22 ALLOSTERIC ENZYMES ALLOSTERIC ENZYMES Is an enzyme with two or more protein POSITIVE REGULATOR – increases the chains (quaternary structure) and two enzyme activity. kinds of binding/active sites ( substrate NEGATIVE REGULATOR – decreases and regulator) the enzyme activity. REGULATOR - these are molecules or (noncompetitive inhibitor) substances that binds on the regulatory sites. 23 24 4 25 26 EXAMPLE OF POSITIVE ALLOSTERIC CONTROL FEEDBACK CONTROL Is a process in which activation or inhibition of the first reaction sequence is controlled by a product of the reaction sequence. 27 28 PROTEOLYTIC ENZYMES AND FEEDBACK CONTROL ZYMOGENS PROTEOLYTIC ENZYME – is an enzyme that catalyzes the breaking of peptide bonds that maintain the primary structure of protein. They are generated in inactive form but converted back to active form as need arises. 29 30 5  PROTEOLYTIC ENZYMES AND PROTEOLYTIC ENZYMES AND ZYMOGENS ZYMOGENS ZYMOGENS – is the inactive form of EXAMPLE: proteolytic enzyme (proenzyme) conversion of pepsinogen to pepsin The names of zymogens can be recognized by the suffix -ogen or the prefix pre- or pro-. 31 32 COVALENT MODIFICATION Is a process in which enzyme activity is altered by covalently modifying the structure of the enzyme through attachment of a chemical group or removal of chemical group from a particular amino acid within enzyme structure. 33 34 COVALENT MODIFICATION The most encountered type is the phosphorylation and dephosphorylation reaction – addition or removal of phosphate group from an enzyme. Antibiotics that Inhibit Enzyme Activity 35 36 6  ANTIBIOTICS ANTIBIOTICS These are substances that kills bacteria EXAMPLES; or inhibits their growth. Sulfa drugs Exert their action selectively on bacteria Penicillins and do not affect the normal Cipro metabolism of the host mechanism. 37 38 SULFA DRUGS Discovered by German bacteriologist Gerhard Domagk (1895-1964) in 1932 by observing the antibacterial activity of sulfanilamide. First “antibiotics” used in the medical field. 39 40 SULFA DRUGS SULFA DRUGS Sufanilamide inhibits bacterial growth Many bacteria needs PABA to because it is structurally similar to PABA synthesize folic acid for growth. 41 42 7  SULFA DRUGS SULFA DRUGS Sulfanilamide acts as competitive Sulfa drugs only inhibit bacterial inhibitor to enzymes in biosynthetic metabolism and growth but not on pathway for converting PABA to folic humans because humans can absorb acid thus led to folic acid deficiency. folic acid from the diet and do not use PABA for its synthesis. 43 44 PENICILLINS PENICILLINS Accidentally discovered by Alexander Penicillin structures (natural and Flemming in 1928 while working on synthetic) contains a four-membered straphylococcus bacteria. beta-lactam ring fused to a five- Most widely used type of antibiotics membered thiazolidine ring. Howard Flowry and Ernst Chain isolated its pure form and proved its effectiveness as antibiotics. 45 46 PENICILLINS Penicillins inhibit transpeptidase, an enzyme that catalyzes formation of cross-links between polysaccharide strands in bacterial cell walls. Cross-links strengthen the bacterial cell walls, prevents lysis. 47 48 8  PENICILLINS PENICILLINS Penicillin’s unique ability of deactivation depends on two important aspects; Similarity of the enzyme’s natural substrate Formation of irreversible inhibition via the reactive amide bond. 49 50 PENICILLINS PENICILLINS Some bacteria develops resistance by Penicillin do not usually interfere with producing penicillinase which normal metabolism in humans because catalyzes the reactive β-lactam ring of its high selectivity towards binding before it can bond with transpeptidase. bacterial transpeptidase. Methicillin and amoxicillin are resistant to penicillinase activity hence clinically important. 51 52 CIPRO CIPRO Clinically known as ciprofloxacin Considered one of the best antibiotics hydrochloride. available because bacteria are slow to Effective agent (broad spectrum) acquire resistance to Cipro. antibiotics. Very effective against anthrax, which skin, bone, urinary, respiratory, and made a Cipro a prominent antibiotic gastrointestinal infections because of biochemical threats associated with terrorism. 53 54 9  CIPRO Cipro is believed to inhibit DNA gyrase – the enzyme responsible for coiling of DNA bacterial chromosome into tertiary structure. When coiling is disrupted, the bacterial DNA cannot replicate and transcribe. Medical Uses of Enzymes 55 56 MEDICAL USE MEDICAL USE Enzymes can be used to diagnose In principle, if those exclusive enzyme certain diseases. will appear in the blood, it may indicate Although blood serum contains many a “damage” or abnormalities in the enzymes, some are not normally found tissue or organ, since the enzyme leaks in the blood but produced only inside into the bloodstream. the cells of certain organs and tissues. 57 58 MEDICAL USE MEDICAL USE Enzymes can be also used in treatment of certain diseases. EXAMPLE: Treating heart attacks with TPA of tissue plasminogen activator which will dissolve the blood clots in the heart and provides relief. 59 60 10  MEDICAL USE Enzymes can be also used in clinical laboratory analysis. EXAMPLE: BUN test (blood urea nitrogen) that measures urea concentration in the blood. High urea concentration in the blood indicates kidney malfunction. 61 11