How do Enzymes Catalyze Reaction

 

How do Enzymes Catalyze Reaction

Each enzyme has an active site to which substrate binds and forms a short-lived highly reaction enzyme substrate complex. This is followed by enzyme product complex (EP). Finally the enzyme product complex dissociates in to product (P) and the enzyme freed, remains unchanged and able to bind more substrate molecules

 Substrate and active site binding mechanism    

The formation of the ES complex is essential for catalysis

E + S = ES ---- EP --- E + P

The catalytic cycle of an enzyme can be described as:

01.The substrate binds to the active site of enzyme.

02.The binding of the substrate induces the enzyme to alter its shape and fit tightly around the substrate.

03.The active site of the enzyme which is in close proximity of the substrate break the chemical bond of the substrate and an enzyme product complex is formed.

04.The enzyme releases the product of the reaction and the free enzyme is ready to take up another molecule of substrate

 

FACTORS AFFECTING ENZYME ACTIVITY

Enzymes are proteins with tertiary structure. Any change in tertiary structure would

affect the action of enzymes.  Factor which affect enzyme action are as follows:

01.Temperature: Enzyme action is greatly affected by temperature. The temperature.    The temperature at which enzyme show their highest activity is called optimum temperature. Enzyme activity declines both above and below the optimum temperature. At low temperature, enzyme becomes temporarily inactive and increasing the temperature to normal, they regain their lost activity. At high temperature there is a loss of enzyme activity due to protein denaturation. At high temperature kinetic energy of molecules in an enzyme becomes strong to break the weak hydrogen bond present in tertiary structure of enzyme resulting in loss of catalytic activity. This change in structure is called denaturation of enzyme. One an enzyme denatures, it remains inactive as temperature is lowered down.

    The optimum temperature for human enzymes 35 – 40^o C. The enzyme activity decreases with decrease as well as increase in temperature and stops at 0^oC and 80^oC.

02.pH: At optimum pH the activity of enzymes is maximum for most enzymes, the effective pH range is 4-9. Beyond these limit denaturation of enzymes takes places. For example the optimum pH for pepsin is 2 and for trypsin is 8.

03.Concentration of substrate: Increase in substrate concentration, increases the velocity of enzymatic reaction. The reaction soon reaches a maximum velocity (V_max) which is not exceed by further rise in concentration of substrate. This is because, at this stage the enzyme molecules become fully saturated and no active site is left free to bind to additional substrate molecules.

04.Product concentration: Accumulation of the product of enzyme reaction lowers the enzyme activity. Enzyme molecules must be freed to combine with more substrate molecules. Normally the products are quickly removed from the site of formation and reaction does not suffer.