Enzymes are organic catalysts of protein origin produced by living cells which help to speed up or slow down the rate of chemical reactions but remain chemically unchanged at the end of the reaction.


Classes of enzymes

Enzymes are usually classified according to the type of food they act upon. Generally three classes are known.

They are amylases, proteases and lipases.


1) Amylases

Amylases act on carbohydrates (starches and complex sugars) changing them to glucose which the body can absorb. Some amylase enzymes are:

Maltase, sucrase, lactase and ptyalin.

  • Maltase changes maltose to glucose.
  • Sucrase changes sucrose to glucose and fructose.
  • Lactase changes lactose to galactose and glucose.
  • Ptyalin changes starch to maltose sugar.


2) Proteases

Proteases act on proteins changing them into amino acids. Some proteases are pepsin, renin, trypsin and erepsin.


  • Pepsin changes protein to peptones.
  • Renin coagulates milk proteins.
  • Trypsin changes proteins to peptones while erepsin changes peptones to amino acids.


3) Lipases act on fats and oils changing them into fatty acids and glycerol.


Characteristics of enzymes

  1. Enzymes act as catalysts which help to speed up or slow down the rate of most chemical reactions within the body of the organism.
  2. They remain chemically unchanged at the end of the reaction.
  3. They are specific in action, that is, one or a group of enzymes will act on specific substrate. For example, the ptyalin in the saliva can only act on cooked starch changing the cooked starch to maltose sugar. Proteases (protein enzymes) will only act on proteins and nothing else.
  4. Enzymes are required in small quantity. A single molecule of one particular enzyme can change 40,000 molecules of its food in a second.
  5. Enzymes act best over a small range of temperature. They are denatured or destroyed at high temperature and inactive at a very cool tempera ture. Their reactions increase with a rise in temperature of 37 degrees Celsius.
  6. They are pH specific (acidity or alkalinity) and act best at certain level of pH. For example, the stomach enzymes act best in acidic medium while the enzymes of the small intestine act best in alkaline medium.
  7. Most enzyme actions are reversible. For example, starch is changed to sugar and from sugar to starch by enzyme diastase.
  8. Enzymes are retarded by poison or inhibitors.
  9. They are protein in nature.
  10. Some enzymes are inactive and therefore require co-enzymes or agents to activate them. For examples, the enzyme trypsinogen requires enterokinase to activate it into trypsin while pepsinogen requires dilute hydrochloric acid to activate it into pepsin. The activators of inactive enzymes are called zymogens. Thus the zymogens of trypsinogen and pepsinogen are enterokinase and dilute hydrochloric acid respectively.
  11. Enzymes can function outside the body of the organism that produces them.