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Dental enzymes

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Biochemistry
Second Year

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Dental enzymes

  1. 1. INTRODUCTION 1. Enzymes are biological catalysts. 2. Almost all enzymes are proteins. 3. They use their dynamic structure to bind substarates and bring them into optimal orientation to make or break chemical bonds. 4. Almost all briochemical reactions are enzyme-catalysed. 5. Most important properties: a) High catalytic power b) High specificity CO2 + H2O Carbonic H2CO3 anhydrase Enzyme + Substrate E-S E + Prduct Enzyme substrate complex 1
  2. 2. 6. Enzymes work by stabilization of transition states. Biomedical Importance: 1. Many diseases (Errors of Met.) are due to synthesis of abnormal enyzmes. 2. Cell injuries result in leakage of certain enzymes into plasma, the measurement of which is useful in diagnosis. 3. Enzyme therapy 2
  3. 3. BASIC CONCEPTS 1. Enzymes are highly SPECIFIC for: a) Type of reaction b) Type of substrate * No wasteful side reactions Examples: Proteolytic enzymes: H O H O H O H O ----N—C—C—N—C—C--- + H2O ------N—C---C + + H3N—C---C--- H R1 H R2 H R1 O- R2 Peptide Caroxyl Component Amino Component 3
  4. 4. Subtilisin: Not specific for side chain Trypsin: Hydrolyse the peptide bond on the Side of Lys and Arg only. Thrombin: More specific Arginine Glycine DNA PolymeraseI: Highly specific Directed by template, chance of Mismatch 1 in 106 replications. H O H O ---N—C—C--------N—C—C--- H H R2 Lysine or arginine Hydrolysis site H O H O ---N—C—C--------N—C—C--- H H Arginine Glycine Hydrolysis site 4
  5. 5. Optical Specificity Most enzyme are optically specific e.g.: Glycolytic enzymes work on D-isomers. Enzymes that work on amino acid, work mostly on L-isomer. Exception: Isomerases (e.g. epimerase) no optical specificity. 2. Regulation of the Catalytic Activity: a) Feed-back Inhibition: A B C D Z End of product Enzyme inhibited by Z 5
  6. 6. 3.Enzymes in diagnosis: * Non-functional plasma enzymes: * Cellular necrosis non-functional enzymes useful in diagnosis Examples: 7
  7. 7. Serum Enzyme Major Diagnostic Use Aminotransferases Aspartate aminotransferase (AST, or SGOT) Alanine aminotransferase (ALT, or SGPT) Myocardial infarction Viral hepatitis Amylase Acute Pancreatitis Ceruloplasmin Hepatoenticular degeneration (Wilson’s disease) Creatinine phosphokinase Muscle disorders and myocardial infarction. γ-Glutamyl transpeptidase Various liver diseases Lactate dehydrogenase (isozymes) Myocardial infarction Lipase Acute pancreatitis Phosphatase, acid Metastatic carcinoma of the prostate Phosphatase, alkaline (isozymes) Various bone disorders, obstructive liver diseases. 8
  8. 8. 4. ENZYME KINETICS The active site: * The site for substrate attachment * It contains amino acid involved directly in making or breaking of chemical bonds. Properties of active site: * Small * It is 3-dimensional * Substrate bind to E by multiple weak bonds (electrostatic, H- bonding, Van der Waals and hydrophobic bonds). * Clefts, H2O is excluded. * Specificity depends on arrangement of atoms in active stie. 12
  9. 9. Transformation of Energy by Enzymes Light Energy Chemical bond energy Food Small molecules. ATP Chemical Energy Mechanical Energy Photo- Synthesis digestion Metabolism Muscle 15
  10. 10. Free Energy: Ist Law of Thermodynamics: Total energy of a system and its surrounding is constant. ∆E = EB—EA = Q ---- W ∆E depends on initial and final states. 2nd Law (Prediction of spontaneity) Condition for a spontaneous process: ∆s System + ∆s surrounding > 0 16
  11. 11. 600 C 200 C 400 C 400 C 1 M NaCL H2O 0.5 M NaCL 0.5 M Nacl Figure 8-6 Processes that are driven by an increase in the entropy of a system : (A) diffusion of heat; and (B) diffusion of a solute. A B 17
  12. 12. Gibbs Free Energy Gibbs combined the 2 laws: ∆G = ∆H - T ∆S ∆G= ∆E - T ∆ S For a reaction if ∆G is negative, the reaction is spontaneous. If ∆G = O, Equilibrium If ∆G is positive, no spontaneity Glucose CO2 + H2O Glucose CO2 + H2O Combustion Enzymes Same ∆G 18
  13. 13. K1[E][S] = (k1 + k3) [ES] [ES] = Km = [ES] = [E][S} K2 + k3 + k1 K2 + k3 k1 [E] [S] KM [E] = [ET] – [ES] [ES] = ([ET] - [ES]) [S] / KM [ES] = [ET] [S] / Km 1 + [S] / Km [ES] = [Et] [S] [S] + Km Substitute for [ES] in equation (1) V = k3 [Et] [S] [S] + Km V = Vmax S S + Km Michaelis-Menten equation 25
  14. 14. Significance of Km Range of Km 10-1 - 10-7 M Km has 2 meanings: i) [S] which fill ½ active sites (1/2 Vmax) ii) Under certain conditions, the Km is a measure of strength of ES complex (affinity). Km = , if K2 >>k3 then Km = = KES = K2 + k3 k1 k2 k1 [E][S] [ES] 27
  15. 15. KES = Dissociation constant of ES If Km is high weak binding of E + S If Km is low strong binding E + S Significance of Vmax: Vmax reveals the turn-over number for an enzyme which is the number of subst. Molecules converted into product by one enzyme molecule in unit time. Vmax = k3[Et], k3 = turnover number 28
  16. 16. Enzyme Inhibition of Enzymes: • Used by cells for regulation • Many drugs and toxins act by inhibition of enzymes. 1. Irreversible Inhibition H3C—C CH3 O ----CH2OH + F---P=O O H3C---C H isopropylphosphofluoridate (DIPF) H H3C---C---CH3 O CH2—O—P—O + HF O H3C---C---CH3 H Enzyme Action of a nerve agent on Acetylcholinesterase Inactivation of acetylcholineserase by diisopropylphosphofluoridate (DIPF) 29
  17. 17. B. Non-Competitive Inhibition: • Act by decreasing the turnover number • Vmax decreased, Km, same. E ES E + P E1 ESI +S + I +S + I 31

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