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Classes of Enzymes

Classes of Enzymes. According to chemical reaction Oxidoreductases: oxidation/reduction reactions Transferases: group transfer reactions Hydrolases: hydrolytic reactions Lyases: addition of groups to double bonds or vice-versa Isomerases: group rearrangements

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Classes of Enzymes

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  1. Classes of Enzymes • According to chemical reaction • Oxidoreductases: oxidation/reduction reactions • Transferases: group transfer reactions • Hydrolases: hydrolytic reactions • Lyases: addition of groups to double bonds or vice-versa • Isomerases: group rearrangements • Ligases: combination of two molecules with involvement of adenosine 5’-triphosphate (ATP) • Grouped by substrate affected • Proteases: proteins • Lipases: lipids (fats) • Carbohydrases: carbohydrates (sugars, starches)

  2. Changes produced by enzymes • Desirable changes • Formation of cheese curd by rennin • Contact lens cleaning by microbial protease • Protein digestion by pepsin, trypsin • Development of flavour in cheese by lipase, esterase • Prevention of staling in bread by amylase • Production of beer by amylase, glucoamylase, protease (in yeast) • Production of low- and no-lactose dairy products (for people with lactose intolerance) by lactase

  3. Undesirable changes • Rotting of foods by protease • Development of rancidity in fats by microbial lipase • Over-ripening of fruits by polygalacturonase • Softening of unblanched vegetables by peroxidase • Development of off-flavours in unblanched vegetables by catalase, lipoxygenase • Browning of certain fruit and vegetable slices by polyphenolase

  4. Substrate + Enzyme Substrate-Enzyme Complex Product + Enzyme Enzyme action

  5. Two models of enzyme action

  6. Heat inactivation Optimum Temperature Effect of temperature on enzyme activity

  7. Optimal pH Effect of pH on enzyme activity

  8. Maximum Enzyme Activity Effect of substrate concentration on enzyme activity

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