Enzymes, their characteristics and importance

  • Enzymes are organic compounds (mostly proteins) produced by the living cells to speed up the spontaneous biochemical reactions in and outside the cells in living organisms.
  • The process of speeding up the chemical reaction is called catalysis, and the substances that speed up the reactions are termed catalytic compounds or catalysts.
  • As the enzymes are secreted by living cells and speed up the chemical reactions, they are known as biocatalysts.
  • The reactants in an enzyme-catalyzed reaction are called the enzyme’s substrates and the substances produced in the reaction are called products.
  • The study of the composition and function of the enzymes is known as enzymology and the expert or specialist in enzymes is called an enzymologist.

Properties or characteristics of enzymes:

  1. Chemical nature
    • Enzymes are generally complex macromolecules of globular proteins.
    • Many enzymes have additional non-protein (inorganic or organic) substances associated with them for their activity called co-factors.
  2. Molecular weight:
    • Being protein macromolecules, enzymes have very high molecular weight.
    • They vary from 6000 from bacterial Ferrodoxin to 4,600,000 for pyruvate dehydrogenase complex.
  3. Chemical activity:
    • Enzymes don’t start a chemical reaction but only accelerate it.
    • They may break a large molecule into two smaller molecules, or bring two small molecules together to form a larger molecule, or transfer whole groups, such as amino group, or transfer electrons or hydrogen ions from one molecule to another.
  4. Changeless form:
    • Enzymes combine temporarily with the substrate molecules but are not consumed or changed permanently in the reaction they catalyze.
    • Their presence doesn’t alter the nature and quantity of the end products of the reaction.
    • The concentration and chemical composition of enzymes remain the same at the end of the reaction.
  5. Reversibility of reaction:
    • Enzyme- controlled reactions are reversible.
    • Enzymes affect only the rate of the biochemical reactions, not the direction.
    • They can accelerate reactions in either direction.
    • For example, lipase can catalyze the splitting of lipids into fatty acids and glycerol as well as synthesis of lipids from glycerol and fatty acids.
    • However, reversion of the reaction may be checked by removing the products of the enzyme reaction as quickly as they are formed.
  6. High efficiency:
    • Most enzymes have high turnover number.
    • A turnover number of an enzyme refers to the number of molecules of substrate acted upon by one molecule of enzyme per minute.
    • For example, a molecule of the enzyme catalase from cattle liver decomposes 5,000,000 molecules of hydrogen peroxide to water and oxygen in one minute at 00C. The turnover number of catalase is thus 5,000,000 at 00C.
    • The turnover number of carbonic anhydrase present in RBCs is 36 million.
    • The higher the turnover number, the more efficient the enzyme is.
    • High turnover numbers of enzymes explain their remarkable effectiveness even though they occur in a cell in minute quantities.
    • Not all enzymes are fast acting. Some are very slow. Lysozyme, for example, catalyzes one reaction every two seconds.
  7. Action specificity:
    • Enzymes are specific in action.
    • An enzyme may catalyze only a particular kind of reaction, or may even act on a particular substrate only.
    • For example, lactase catalyzes the hydrolysis of lactose and no other disaccharide.
    • Specificity of enzymes results from their unique 3-dimensional shape.
  8. Temperature sensitivity:
    •  Enzymes are thermolabile, i.e. heat sensitive.
    • They function best at an optimum temperature. The optimum temperature for human enzymes is 35-40 00C, i.e. close to human body temperature.
    • The enzyme activity decreases with the decrease as well as increase in the temperature and stops at 00C and above 80 0C.
    • The enzymes of bacteria inhabiting hot springs have an optimum temperature of 700C or more.
  9. pH sensitivity:
    • Enzymes show maximum activity at an optimum pH (6-8).
    • Their activity slows with the increase and decrease in pH till it stops.
    • For example, pepsin, a digestive enzyme in the stomach, works best at pH 2. This high acidic pH denatures most of the enzymes but pepsin is adapted to it.
  10. Team work:
    • Enzymes generally work in teams inside the cell, the product of one enzyme-controlled reaction serving as the substrate for the next.
    • In germinating seeds, starch is changed into glucose by two enzymes; amylase and maltase. Amylase splits starch into a double sugar maltose, which is then broken down by maltase into single sugar glucose.
    • Eleven different enzymes work sequentially to convert glucose to lactic acid in animals as well as in plants.
  11. Destruction by poisons:
    • Enzymes are destroyed by poisons, such as cyanide and iodoacetic acid. Cyanide poisoning is due to the destruction of the respirator cytochrome enzyme by the cyanide.

Importance or uses of enzymes:

  • Biological uses:
    • A large number of chemical reactions take place in the living cells all the time. The reactions would normally occur outside the cells only at temperatures high enough to literally burn up the cells, or would occurs so slowly as to be useless, being unable to sustain life.
    • Enzymes help in many biological processes:
      1. Physiology:
        • Enzymes digest food in alimentary canal of animals which will starve without the enzymes.
        • The enzymes are also essential for respiration, blood clotting, muscle contraction, nerve impulse transmission and so on.
        • A missing or defective enzyme can be very harmful. Lack of sucrase causes abdominal pain and diarrhea in people eating sucrose.
        • Thus, the enzymes help in carrying out all our essential biochemical reactions and make life possible.
      2. Medical diagnoses:
        • ELISA (Enzyme-linked immune sorbent assay) is used for detecting diseases such as HIV, hepatitis etc. by using specific enzymes.
      3. Medical treatment:
        • Enzyme streptokinase is used in dissolving blood clot formed inside blood vessels.
      4. Digestive aids:
        • Enzyme diastase along with other enzymes is used as digestive aid in patients with faulty digestive juices.
      5. Genetic engineering:
        • Enzymes, such as endonucleases, ligases, etc. are used in genetic engineering for breaking down and joining DNA fragments.
  • Industrial uses:
    • Some of the enzymes have a great industrial value too.
      1. Alcoholic drinks:
        • Enzymes zymase obtained from yeast is used in making alcoholic beverages by fermentation of sugary substances.
      2. Cheese:
        • Enzyme rennin procured from calf’s stomach is used in making cheese by coagulating milk protein caseinogen.
      3. Detergents:
        • Detergents for washing clothes contain an enzyme protease.
      4. Cleaning of hides:
        • Enzyme protease is used for cleaning hides of animals and softening of meat.
      5. Clearing of fruit juices:
        • Enzyme pectinase is used for clearing fruit juices.
      6. Baby food:
        • Enzyme trypsin is added to predigest baby foods partly.
      7. Waste treatment:
        • Bacteria in a box of cat’s litter (waste matter) produce the enzyme urease that catalyzes the breakdown of urea (from urine) to carbon dioxide and ammonia.
      8. Enzymes are also used for retting of fibers, degumming of silk, food processing and synthesis of various chemicals in the industries.

Enzymes, their characteristics and importance