Enzyme Catalysis

Enzymes

Large number of organic reactions are taking place in the body of animals and plants to maintain the life processes. These reactions are catalysed by complex nitrogenous organic compounds  known as enzymes.

These are also called biological catalysts or biochemical catalysts and are produced by the living cells in plants and animals.

Thus, enzymes are biological catalysts produced by living cells which catalyze the biochemical reactions in living organisms. Chemically all enzymes are proteins with molar mass ranging from 15,000 to 1,000,000 g/mol. Without enzymes, the living processes would be very slow to sustain life. 

 

Common examples of enzyme catalysis reactions

(1) Normal conversion of glucose into ethanol by zymase (enzyme) present in yeast.

C₆H₁₂O₆ ——> 2C₂H₅OH + 2 CO₂

(2) Hydrolysis of urea (NH₂CONH₂) by urease (enzyme) present in soyabean.

NH₂CONH₂ + H₂O —–> 2 NH₃ + CO₂ 

(3) Hydrolysis of starch into maltose by diastase (enzyme).

2 (C₆H₁₀O₅)n + n H₂O (l) ——> nC₁₂H₂₂O₁₁

(4) Conversion of maltose into glucose by maltase (enzyme).

C₁₂H₂₂O₁₁ + H₂O (l) ——> nC₆H₁₂O₆

(5) Hydrolysis of sugar into glucose and fructose by invertase (enzyme) present in yeast.

C₁₂H₂₂O₁₁ + H₂O (l) ——>  C₆H₁₂O₆ + C₆H₁₂O₆

(6) Oxidation of alcohol to acetic acid by micoderma aceti.

C₂H₅OH + O₂ —-> CH₃COOH + H₂O

(7) Decomposition of urea into ammonia and carbon dioxide by urease enzyme.

NH₂CONH₂ + H₂O(l) ——> 2NH₃ (g) + CO₂ (l) 

(8) In stomach the pepsin enzyme converts proteins into peptides whereas in intestine, the pancreas trypsin converts proteins into amino acids by hydrolysis.

(9) Milk is converted into curd by the enzymatic reaction brought about by lacto bacilli enzyme present in curd.

Characteristics of Enzyme Catalysts

1) High efficiency

Enzyme catalysts increase the speed of reactions by 10⁸ to 10²² times as compared to the uncatalysed reactions. The enzymes are highly efficient and one molecule of enzyme may transform one million molecules of the reactant per minute.

2) Extremely small quantities

Extremely small quantities of enzyme catalysts-as small as millionth of a mole-can increase the rate of reaction by factors of 10³ to 10⁶.

3) Specificity

The enzyme catalysts are highly specific in nature. Almost every biochemical reaction is controlled by its own specific enzymes.

For example : urease catalyses the hydrolysis of urea 

NH₂CONH₂ + H₂O(l) ——> 2NH₃ (g) + CO₂ (l) 

Similarly, maltase catalyses the hydrolysis of maltose. 

 

4) Optimum temperature

The rate of an enzyme reaction becomes maximum at a definite temperature known as the optimum temperature.

For example: the enzyme catalysts are active at moderate temperature 298-310 K and the
human body temperature (310 K) is suited for enzyme catalysed reactions.

5) Optimum pH

The rate of an enzyme catalysed reaction is maximum at a particular pH called optimum pH. This is between pH values of 5- 7.

6) Control of activity of enzymes

The action of enzyme catalytic reactions are controlled by various mechanisms and are inhibited by various organic and inorganic molecules.

7) Regulated activity

The activity of most enzyme catalysts is closely regulated.

8) Increasing activity in the presence of activators or coenzymes

Catalytic activity of enzymes is greatly enhanced by the presence of activators or coenzymes.

Activators are metal ions (Na⁺, Mn²⁺, Co²⁺, Cu²⁺ etc.) which get weakly bonded to enzyme molecules and therefore, promote their catalytic action.

Most active enzymes are associated with some non-protein components (vitamins) required for their activity. These are generally metal ions or small organic molecules and are collectively called coenzymes.

The common metal ions are Zn, Mg, Mn, Fe, Cu, Co, Mo, K and Na.

9) Influence of inhibitors and poisons

The enzyme activity can be reduced or inhibited by the presence of certain compounds known as enzyme inhibitors or poisons. These inhibitors or poisons interact with the active functional groups on the enzyme surface and
often reduce or completely destroy the catalytic activity of the enzymes. The use
many drugs is related to their action as enzyme inhibitors in the body.