Enzymes Part I: Introduction, different types of properties, chemical nature


In this article you will find full details of enzymes. You will know the history of enzyme, different types of properties of enzymes and chemical nature of enzymes. you will also understand the difference between apoenzyme and co-factor.

Introduction

Enzymes are biocatalysts of proteinous nature, which accelerate the rate of biochemical reactions but do not affect the nature of final product. Like catalyst the enzymes regulate the speed and specificity of reaction without being used up but unlike catalysts enzymes are produced by the living cells only. Like catalysts enzymes also influence the rate of biochemical reaction so that they can take place at a relatively low temperature. Thus the enzymes are known to lower the activation energy. In many cases enzymes initiate the biological reaction.

The term enzymes is derived from Greek word enzymes which means 'in yeast' because the yeast cells were first to reveal the enzyme activity in living organisms. The term enzyme was coined by W. Kuhne in the year 1878.

Properties of Enzymes

Properties of enzymes can be classified into three groups:

  • Physical properties
  • Chemical Properties
  • General properties

Physical Properties of Enzymes

The physical properties of enzymes are:

  • Physically enzymes behave as colloids or as substance of high molecular weight.
  • Enzymes are destroyed or inactivated at temperature below the boiling point of water.
  • At 60 degree Celsius most enzymes in liquid medium are inactivated.
  • Dried enzymes extract can endure temperature 100 degree Celsius to 120 degree Celsius or even higher. Thus enzymes are thermolabile.
  • There is always a specific temperature of optimum activity of every enzyme, which usually ranges from 25 degree Celsius to 45 degree Celsius. Enzymatic action is highest at 37 degree Celsius and enzymes become inactive when temperature rises above 60 degree Celsius.

Chemical Properties of Enzymes

There are two main chemical properties of enzymes:

  1. Catalytic properties : Enzymes are biological catalyst. The small quantity of enzymes catalyses the larger quantities of substances. It means, enzymes have high capability to convert large quantities of substrate into product. Enzymes increase the rate of reaction and remain unaffected by the reaction which they catalyze.
  2. specificity of enzyme : Enzymes are highly specific in nature, i.e., a particular enzyme can catalyze a particular reaction. For example, Enzyme sucrase can catalyze only hydrolysis of sucrose.

General Properties of Enzymes

General properties of enzymes are:

  • Enzymes initiate and accelerate the rate of biochemical reaction.
  • The activity of enzymes depends upon the acidity of medium (pH specific). Each enzyme is most active at a particular pH. For example, pH 2 for pepsin, pH 8.5 for trypsin. Most intracellular enzymes function at near neutral pH.
  • Enzymes can accelerate the reaction in either direction.
  • All enzymes possess active sites which participate in the biochemical reactions.
  • Enzymes are very unstable compounds mostly soluble in water, dilute glycerol, NaCl and dilute alcohol.
  • Enzymes act actively at optimum temperature.
  • All enzymes are proteinous in nature but all proteins may not be an enzyme.
  • Enzymes lower the energy of activation of the substance molecule so the biochemical reaction can take place at normal body temperature which is 37 degree Celsius.

Chemical Nature of Enzymes

All enzymes are proteins, but all proteins are not enzymes. However, there are some conjugated enzymes with a non protein moiety attached to the protein part of enzyme, which is called apoenzyme. The non protein part is known as co factor. If the co factor is of inorganic nature like potassium calcium, magnesium, manganese it is known as prosthetic group. Prosthetic group is generally tightly bound to the protein part of enzyme and it is difficult to separate it with simple method like diffusion. The enzyme with prosthetic group and apoenzyme is called holoenzyme.

If co factor attached to an enzyme protein is organic moiety like NADP, NAD, FAD, etc , it is called coenzyme. A co enzyme is generally loosely bound to apoenzyme and can easily be separated than prosthetic group. Co enzymes are heat resistant also.

Difference between apoenzyme and co-factor

The difference between apoenzyme and co-factor are as follows:

  1. Apoenzyme is protein part of enzyme hence a macromolecule whereas co factor is the non protein part of enzyme hence a micromolecule.
  2. Apoenzyme is an enzyme which acts only in presence of a co-factor whereas co-factor may be metal ion or a complex organic compound makes an apoenzyme functional.
  3. Apoenzyme is thermolabile whereas co-factor is thermostable.
  4. Apoenzyme conducts enzymatic activities whereas co-factor moulds the enzyme or co enzyme or carries the groups removed from the substrate.
  5. Apoenzyme is specific for an enzyme system whereas co-factor work with many enzymes.

Conclusiong

So in this article you read about enzymes, their properties, chemical nature and comparison of apoenzyme with co-factor. You will read comparison of enzyme and catalyst, nomenclature of enzyme and biological significance of enzymes in enzyme part II .


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