Enzymes

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  • 1. Compiled & Edited by Dr Syed Ismail, MKV Parbhani Enzymes Compiled & Edited by Dr. Syed Ismail VN Marathwada Agril. University, Parbhani, India 1
  • 2. Compiled & Edited by Dr Syed Ismail, MKV Parbhani 2 Enzymes are complex chemicals that control reactions in living cells. They are biochemical catalysts speeding up reactions that would otherwise happen too slowly.
  • 3. Compiled & Edited by Dr Syed Ismail, MKV Parbhani 3 • Biological catalysts – a molecule which speeds up a • • • • • chemical reaction but remains unchanged at the end of the reaction Generally names end in –ase Globular proteins (soluble) Active site – region (cleft or depression) to which another molecule or molecules (substrate) can bind Substrate fit perfectly and is held in place by temporary bonds which form between the substrate and some of the R groups of the enzyme’s amino acids (enzymesubstrate complex) Specific - shape of active site will only allow one shape of molecule to fit
  • 4. Compiled & Edited by Dr Syed Ismail, MKV Parbhani 4 The Chemical nature of enzymes Enzymes are globular proteins. They have a complex tertiary and quaternary structure in which polypeptides are folded around each other to form a roughly spherical or globular shape. The overall 3D shape of an enzyme molecule is very important: if it is altered, the enzyme cannot bind to its substrate and so cannot function. Enzyme shape is maintained by hydrogen bonds and ionic forces. Enzymes have several important properties: Enzymes are specific: each enzyme usually catalyses only one reaction. Enzymes combine with their substrates to form temporary enzyme-substrate complex. Enzymes are not altered or used up by the reactions they catalyze, so can be used again and again. Enzymes are sensitive to temperature and pH. Many enzymes need cofactors in order to function. Enzyme function may be slowed down or stopped by inhibitors.
  • 5. Compiled & Edited by Dr Syed Ismail, MKV Parbhani < TD> 5
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  • 7. Compiled & Edited by Dr Syed Ismail, MKV Parbhani 7 NOMENCLATURE ENZYME SUBTRATE or REACTION TYPE Maltase Maltose Urease Urea Proteases Proteins Carbohydrases Carbohydrates Lipases Lipids Hydrolases Hydrolysis Reaction Deaminases Removing amines Dehydrogenases Removing hydrogens
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  • 9. 9 OXIDOREDUCTASES CATALYZE REDOX REACTIONS SOME COMMON TYPES: – – – – REDUCTASES DEHYDROGENASES OXIDASES OXYGENASES LOOK FOR INVOLVEMENT OF COENZYMES – NAD+ , NADP+, FAD, FMN
  • 10. 10 TRANSFERASES TRANSFER OF FUNCTIONAL GROUPS SOME EXAMPLES: – TRANSFERASES – PHOSPHORYLASES TRANSFER OF Pi OR PPi – KINASES A PHOSPHATE TRANSFER UTILIZE OR GENERATE ATP
  • 11. 11 HYDROLASES HYDROLYSIS REACTIONS WATER MOLECULES USED TO BREAK BONDS EXAMPLES: – PHOSPHATASES – PEPTIDASES – ATPase, GTPase
  • 12. 12 LYASES CATALYZES REACTIONS THAT – GENERATE A DOUBLE BOND – ADDS A SUBSTRATE MOLECULE TO DOUBLE BOND OF A SECOND SUBSTRATE EXAMPLES: – DECARBOXYLASES – DEHYDRATASES – ALDOLASE
  • 13. 13 ISOMERASES CONVERSION OF ONE ISOMERIC FORM INTO ANOTHER EXAMPLES: – – – – ISOMERASES EPIMERASES RACEMASES MUTASES
  • 14. 14 LIGASES TWO MOLECULES ARE JOINED ANABOLIC REACTIONS REQUIRE NUCLEOTIDES (ATP, GTP) TO DRIVE THEM – A PYROPHOSPHATE BOND MUST BE BROKEN EXAMPLES: – CARBOXYLASE – SYNTHETASES
  • 15. Compiled & Edited by Dr Syed Ismail, MKV Parbhani Activation energy • Enzymes increase the rate at which chemical reactions occur • Activation energy – extra energy temporarily given to substrate to convert it to product 15
  • 16. Compiled & Edited by Dr Syed Ismail, MKV Parbhani 16  Like all catalysts, enzymes work by lowering the activation energy for a reaction, thus dramatically accelerating the rate of the reaction.  Most importantly;Enzymes are not used up by the reaction. After they have done their work they release the products and are not changed.
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  • 18. Compiled & Edited by Dr Syed Ismail, MKV Parbhani How do enzymes Work? Enzymes work by weakening bonds which lowers activation energy 18
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  • 20. 20 • Vmax occurs when enzyme active sites are saturated with substrate • Km (Michaelis-Menten constant) reflects affinity of enzyme for its substrate • smaller the Km, the greater the affinity an enzyme has for its substrate
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  • 39. Compiled & Edited by Dr Syed Ismail, MKV Parbhani 39 FACTORS AFFECTING ENZYME ACTIVITY Following are the important factors affecting the enzyme activity. Temperature pH Salt & Inorganic ions Enzyme concentration Inhibitors Cofactors and coenzymes
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  • 49. Compiled & Edited by Dr Syed Ismail, MKV Parbhani 49 Inhibitors  Inhibitors slow down or stop enzyme reaction. Usually, enzyme inhibition is a natural process, a means of switching enzymes on or off when necessary.  Inhibition can be reversible and the enzyme returns to full activity once the inhibitor is removed. Drugs and poisons can inhibit particular enzymes, this type of inhibition is often non-reversible.  Reversible inhibitors are either competitive or non-competitive.  Competitive inhibitors Compete with normal substrate molecules to occupy the active site. A competitive inhibitor fits into the active site of the enzyme preventing the real substrate from gaining access. The inhibitor cannot be converted to the products of the reaction and so the overall rate of reaction is slowed down.
  • 50. Compiled & Edited by Dr Syed Ismail, MKV Parbhani 50 Competitive Inhibition This is where the inhibitor is a molecule which has a similar shape to the molecule which is supposed to be binding to the active site. In the case of enzymes, a competitive inhibitor may have the same shape as that of the substrate, but it doesn't react in the same way. Rather than turning into the product, it simply uses up time and prevents the substrate from getting to the active site. It blocks the way.
  • 51. Compiled & Edited by Dr Syed Ismail, MKV Parbhani 51 Non-competitive Inhibition • This is the kind that exists when a molecule binds to a different site on the enzyme, rendering it inactive. Sometimes it does this before the substrate reaches the active site, sometimes afterwards, but in either case it stops the enzyme doing its job, and prevents a product being formed.
  • 52. Compiled & Edited by Dr Syed Ismail, MKV Parbhani 52 • In both competitive and non-competitive inhibition, • it is possible to have both reversible and irreversible inhibitors. • As the name suggests, a reversible inhibitor does not have a permanent affect - it will stop the enzyme doing what it is supposed to do, • but it will move off again and allow the enzyme to function later on; • an irreversible inhibitor, on the other hand, permanently renders the enzyme inactive, so it will have to be replaced by a brand new one . ALBIO9700/2006JK
  • 53. Compiled & Edited by Dr Syed Ismail, MKV Parbhani End-product inhibition 53
  • 54. Compiled & Edited by Dr Syed Ismail, MKV Parbhani 54 Cofactors and Coenzymes • Inorganic substances (zinc, iron) and vitamins (respectively) are sometimes need for proper enzymatic activity. • Example: Iron must be present in the quaternary hemoglobin in order for it to pick up oxygen. structure - 54
  • 55. Compiled & Edited by Dr Syed Ismail, MKV Parbhani 55
  • 56. Compiled & Edited by Dr Syed Ismail, MKV Parbhani 56 APOENZYMES and COENZYMES Coenzymes are not proteins and so are not inactivated by heat. Examples of coenzymes are the vitamins or compounds derived from vitamins. The reaction involving a coenzyme can be written as follows: coenzyme + apoenzyme = enzyme Coenzyme A is essential in the metabolism of carbohydrates, lipids, and proteins in the body.
  • 57. Compiled & Edited by Dr Syed Ismail, MKV Parbhani 57 •Coenzymes are bound at the active site in order to interact with the substrate and play an essential role in the catalysed reaction. •They act as carriers of a variety of chemical groups.
  • 58. Compiled & Edited by Dr Syed Ismail, MKV Parbhani 58 Most water-soluble vitamins are components of coenzymes Vitamin Coenzyme Deficiency Thiamine (B1) Thiamine pyrophosphate Beriberi (weight loss,other problems Riboflavin (B2) FAD+ Mouth lesions, dermatitis Nicotinic acid (niacine) NAD+ Pellagra (dermatitis, depression) Pantohtinic acid Coenzyme A Hypertension Biotin Biotin Rash, muscle pain
  • 59. Compiled & Edited by Dr Syed Ismail, MKV Parbhani 59 Zymogen Active Enzyme Function Pepsinogen Chymotrypsinogen Trypsinogen Procarboxypeptidase Proelastase Prothrombin Fibrinogen Factor VII Factor X Proinsulin Procollagen Procollagenase Pepsin Chymotrypsin Trypsin Carboxypeptidase Elastase Thrombin Fibrin Factor VIIa Factor Xa Insulin Collagen Collagenase protein digestion protein digestion protein digestion protein digestion protein digestion blood clot formation blood clot formation blood clot formation blood clot formation plasma glucose homeostasis component of skin and bone remodeling processes during metamorphosis, etc.
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