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Enzymology Jan.pptx
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- 2. CLASSIFICATION OF ENZYMES Class1. Oxidoreductases: Transfer of hydrogen or addition of oxygen. Ex:- Lactate dehydrogenase (coenzyme NAD); Glucose-6-phosphate dehydrogenase (coenzyme NADP); Succinate dehydrogenase (coenzyme FAD); dioxygenases. Class 2. Transferases: Transfer of groups other than hydrogen. Ex:- Aminotransferase. (Subclass: Kinase, transfer of phosphoryl group from ATP; e.g. Hexokinase) Class 3. Hydrolases: Hydrolysis of the bond (Cleave bond and add water); e.g. Acetylcholine esterase, Trypsin and most of the digestive enzymes.
- 3. CLASSIFICATION OF ENZYMES Class4. Lyases: Cleave without adding water, e.g. Aldolase; HMG CoA lyase; ATP Citrate lyase. Class 5. Isomerases: Intramolecular transfers causing optical, geometric isomer formation. They include racemases and epimerases. ex- Triose phosphate isomerase. Class 6. Ligases: ATP dependent condensation (linking of substrates) of two molecules, ex- Acetyl-CoA carboxylase; Glutamine synthetase; PRPP synthetase.
- 4. CLASSIFICATION OF ENZYMES Class7: Translocases A new class of enzymes . Translocases- catalyzes the translocation of ions and other molecules across membranes. ex- There are specific translocases for transferring hydrogen ions, inorganic anions, cations, amino acids.
- 5. Synthetase and Synthase- Difference Synthetases are ATP dependent enzymes catalyzing biosynthetic reactions; they belong to Ligases (class 6). Examples are Carbamoyl phosphate synthetase; Argininosuccinate synthetase; PRPP synthetase and glutamine synthetase. Synthases are enzymes catalyzing biosynthetic reactions; but they do not require ATP directly; they belong to classes other than ligases. Examples are glycogen synthase and ALA synthase.
- 6. COENZYME • These substancesare the • NON PROTEIN • ORGANIC • LOW MOLECULAR WEIGHT • DIALYSIBLE (easily dissociates).
- 7. Salient features ofCoenzymes • It is essential for biological activity of the enzyme. • Coenzyme is a L.M.W. organic substance. • It is heat stable. • Generally, the coenzymes combine loosely with the enzyme molecules. The enzyme and coenzyme can be separated easily by dialysis.
- 8. • When thereaction is completed, the coenzyme is released from the apoenzyme, and is available to bind to another enzyme molecule. • One molecule of the coenzyme is able to convert a large number of substrate molecules with the help of enzyme. • Most of the coenzymes are derivatives of vitamin B complex group of substances.
- 14. Examples of Coenzymes CoenzymeGroup transferred Thiamine pyrophosphate (TPP) Hydroxy ethyl Pyridoxal phosphate (PLP) Amino group Biotin Carbon dioxide Coenzyme A (Co A) Acyl groups Tetrahydrofolate (FH4) One carbon group Adenosine triphosphate (ATP) Phosphate
- 16. Metalloenzymes Metal Enzymecontaining Selenium Glutathione Peroxidase Zinc Carbonic anhydrase, Superoxide Dismutase, carboxy peptidase, alcohol dehydrogenase, RNA polymerase Magnesium Hexokinase, phosphofructokinase, enolase, pyruvate kinase Manganese Phospho-glucomutase, glycosyl transferases Copper Tyrosinase, cytochrome oxidase, lysyl oxidase, superoxide dismutase Iron Cytochrome oxidase, catalase, peroxidase, xanthine oxidase Calcium Phospholipase, lipase Molybdenum Xanthine oxidase
- 17. Mode of Actionof Enzymes 1. Lowering of activation energy 2. Acid base catalysis 3. Substrate strain 4. Covalent catalysis 5. Entropy effect 6. Product Substrate orientation theory 7. Michaelis-Menten theory 8. Fischer’s template theory 9. Koshland’s Induced fit theory
- 18. Lowering of activationenergy by enzymes. Red circle = substrate; D = energy level of product. C to A = activation energy in the absence of enzyme; C to B is activation energy in presence of enzyme; B to A = lowering of activation energy by enzyme.
- 19. During enzyme substratebinding, the interactions get optimized and the substrate plays an important role in enzymatic catalysis- 1. Substrate Strain 2. Acid- Base catalysis 3. Covalent catalysis 4. Entropy effects A combination of 1 or more of them helps in the catalytic activity of several enzymes.
- 20. Acid base catalysis-with the help of Histidine -Glu Asp Cys Ser Tyr
- 21. COVALENT CATALYSIS • Formationof covalent bonding formed by the action of nucleophilic (negatively charged) or electrophilic group of enzymes. • Enzymes having serine residues at the active sites belong to such a group. • Ex -Trypsin, Chymotrypsin, Clotting factors.
- 23. ENTROPY effect • Enzymesenhance the reaction by decreasing the entropy by physical appositioning of the 2 reactants known as the proximity effect. • Enzyme- substrate complex improves the probability of the collision of these these molecules manifold and thus increasing the rate of reaction. Product-Substrate Orientation Theory • Specific orientation of the 3d structure in such a way that there is physical apposition thus leading to higher rate of reaction.
- 24. Correct alignment ofamino acids in the active center of the enzyme.
- 25. MICHAELIS MENTEN THEORY •Lenor Michaelis and Maud Menten had the proposed the theory. • Formation of Enzyme-Substrate complex which breaks down to form the enzyme and product. • Alkaline Phosphatase contains a serine residue active site which hydrolyses phosphate esters.
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- 27. Fischer’s Template Theory -3Dstructure of the active site of the enzyme is complementary to the substrate. Thus enzyme and substrate fit each other. Substrate fits on the enzyme, similar to lock and key. The lock can be opened only by its specific key. Couldn’t explain flexibility of enzymes.
- 28. Koshland’s induced fittheory • Enzyme has shallow grooves; substrate alignment is not correct. • Fixing of substrate induces structural changes in enzyme. • Now substrate correctly fits into the active site of enzyme. • Substrate is cleaved into two products
- 29. • The regionof the enzyme where substrate binding and catalysis occurs is referred to as active site or active centre and these two may be separate. • Although all parts are required for keeping the exact three dimensional structure of the enzyme, the reaction takes place at the active site. The active site occupies only a small portion of the whole enzyme. • Generally active site is situated in a crevice or cleft of the enzyme molecule. To the active site, the specific substrate is bound. The binding of substrate to active site depends on the alignment of specific groups or atoms at active site. ACTIVE SITE OF ENZYMES
- 30. • During thebinding, these groups may realign themselves to provide the unique conformational orientation so as to promote exact fitting of substrate to the active site. • The substrate binds to the enzyme at the active site by noncovalent bonds. These forces are hydrophobic in nature. • The amino acids or groups that directly participate in forming/breaking the bonds (present at the active site) are called catalytic residues or catalytic groups.
- 31. Name of enzymeImportant amino acid at the catalytic site Chymotrypsin His (57), Asp (102), Ser (195) Trypsin Serine, Histidine Thrombin Serine, Histidine Phosphoglucomutase Serine Alkaline phosphatase Serine Acetyl cholinesterase Serine Carbonic anhydrase Cysteine Hexokinase Histidine Carboxypeptidase Histidine, Arginine, Tyrosine Aldolase Lysine Active site of Some Enzymes
- 32. Proteases Type Example Serine proteasesTrypsin, chymotrypsin, clotting factors Aspartic proteases Pepsin Cysteinyl aspartic proteases Caspases in apoptosis Metalloproteases Carboxy peptidases Protease inhibitors used as drugs ACE inhibitor (Captopril), HIV protease inhibitor (Retonavir)
- 33. 1. Exergonic orExothermic Reaction Energy is released from the reaction, and therefore reaction goes to completion, e.g. urease enzyme: Urea → ammonia + CO2 + energy ( irreversible ; product conc. is 99.5%) 2. Isothermic Reaction When energy exchange is negligible, and the reaction is easily reversible. e.g. Pyruvate + 2H Lactate 3. Endergonic or Endothermic Reaction Energy is consumed and external energy is to be supplied for these reactions for these reactions. In the body this is usually accomplished by coupling the endergonic reaction with an exergonic reaction, e.g. Hexokinase catalyzes the following reaction: Glucose + ATP → Glucose-6-phosphate + ADP THERMODYNAMIC CONSIDERATIONS
- 34. Body couples exergonicand endergonic reactions for synthetic reactions.
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