Classes of Enzymes

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
Enzyme action
5
Two models of enzyme action
6
Effect of temperature on enzyme activity
7
Effect of pH on enzyme activity
8
Effect of substrate concentration on enzyme
activity