ENZYMES : CLASSIFICATION, PROPERTIES, EFFECTS,TYPES,FACTORS

ENZYMES :

Enzyme, a substance that acts as a catalyst in living organisms, regulating the rate at which biochemical reactions proceed without itself being altered in the process.

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  CLASSIFICATION OF ENZYMES:

 A) On the basis of site of action:

  i) Exoenzymes / Extracellular enzymes:  These type of enzyme which are Secret outside the cell .                                          E.g..: proteoses, lipases.

  ii) Endoenzymes / Intracellular enzymes: These type of enzyme which are present inside the cell .                E.g..: synthetases, phosphorylases.

 iii) Constitutive Enzymes: 

These type of enzyme which are produced in absence of substrate.      Eg.: Enzymes of glycolytic series.

 iv) Induced Enzymes:                        These type of enzyme which are produced in presence of substrate.     Eg.: hepatic microsomal enzymes.

 v) Zymogens / Proenzymes:                These type of enzyme which are produced naturally in an inactive form which can be activated when required. Enzymes like pepsin are created in the form of pepsinogen, an inactive zymogen. Pepsinogen is activated when Chief cells release it into HCl which partially activates it.  

 B) On the basis of reactions they catalyze: 

 i) Oxidoreductases :

 These type of enzyme which catalyze biological oxidation & reduction between two substrates. e.g ; Hydroxylases, Hydroperoxidases, Dehydrogenases, Oxidases, Oxygenases.

  ii) Transferases :                                      These type of enzyme which catalyzetransfer of some group or radical from one molecule to another. E.g.Transaminases, Transglycosidases, Transphosphorylases. 

iii) Hydrolases: Thes type of enzyme which catalyze hydrolytic cleavage reactionby addition or removal of water. Eg. Esterases, Peptidases.

 iv) Lysases: These type of enzyme which catalyzethe cleavage reaction but they are non-hydrolytice.g. Carboxylysases, Aldehydelysases.

v) Isomerases: Thes type of enzyme which catalyze interconversion of isomers. eg. Dextrose isomerase vi) Ligases/ Synthatases: Thes type of enzyme which catalyze formation of bond .Forming C-S bonds, C-N bonds, C-C bonds.

  

 PROPERTIES OF ENZYMES :  

1. Proteinous nature: Nearly all enzymes are proteins although some catalytically active RNA molecules have been identified.

2. Colloidal nature: In the protoplasm, enzymes exist as hydrophilic colloids. Due to colloidal nature, they are isolated by dialysis.
           
 3. Substrate specificity : A given enzyme only catalyzes one reaction or a similar type of reaction. For example, maltase acts only on maltose while pancreatic lipase acts in a variety of fats. Sometimes, different enzymes may act on the same substrate to produce different end products. The substrate specificity of enzyme is based on amino acids sequence in the catalytic site as well as the optical isomeric form of the substrate.

 4. Catalytic properties:
 i. Enzyme require in small concentration for any chemical change,
 ii. They don’t initiate the catalysis but accelerate the rate of catalysis by lowering the activation energy, 
iii. They remain unchanged at the end of reaction, 
iv. Their presence don’t alter the properties of end products, 
v. Enzymes accelerate the forward or reverse reactions to attain the equilibrium but don’t shift the equilibrium,
 vi. Usually enzyme catalyzed reactions are reversible, but not always, 
vii. They require hydration for activity.

5. Turn over Number (Enzyme efficiency):
 It is the number of substrate molecules changed per unit of time per enzyme. Typical turn over number varies form 102 to 103 sec-1.. Enzyme efficiency is very low in Lysozyme.

6. Sensitivity: Enzymes are highly sensitive to change in pH, temperature and inhibitors. Enzymes work best at a narrow range of condition called optimum.
 (i) Temp: The optimum temp of enzymes is 20-35°C. They become inactivated at very low temperature and denatured (destroyed) at very high temp i.e. greater than 45°C. Low molecular weight enzymes are comparatively more heat stable. In archebacterium Pyrococcus furious, the optimum temperature of hydrogenise is greater than 95°C. This heat-stable enzyme enables Pyrococcus to grow at 100°C.
 (ii) pH: The optimum pH of most endoenzyme is pH 7.0 (neutral pH). However, digestive enzymes can function at different pH. For example, salivary amylase act best at pH 6.8, pepsin act best at pH2 etc. Any fluctuation in pH from the optimum causes ionization of R-groups of amino acids which decrease the enzyme activity. Sometime a change in pH causes the reverse reaction, e.g. at pH 7.0 phosphorylase break down starch into glucose 1- phosphate while at pH5 the reverse reaction occurs.

 7. Inhibitors: Enzymes are sensitive to inhibitors. The chemical substance that combines with the enzymes and inhibits its catalytic activity is called an inhibitor. eg. Cyanides. 

 FACTORS AFFECTING RATE OF ENZYME CATALYZED REACTION : 

 Factors that affect velocity of enzyme catalyzed reaction 
 1. Effect of temperature
 2. Effect of of enzymes concentration 
3. Effect of of substrate concentration
 4. Effect of of Inhibitors
 5. Effect of Time  
6. Products of reaction 
 7. Effect of light & other physical factors 
 8. Allosteric factors  
9. Effect of hormones & other biochemical agents .

Effect of temperature: 

As increase in temperature the rate of reaction / velocity is increased. This increased temperature accelerate an enzyme catalysed reaction. The temperature at which the enzyme shows maximum velocity this temp. is called as optimum temperature is usually reached at around 37oC—45oC.  It means at optimum tem. Enzyme is activating. Or having maximum activity.  Below the optimum temp. Enzyme gets frozen, below 37oC.   Above the optimum temperature (i.e. above45oC), rate get decreases.  The enzyme gets inactivate due to denaturation, hence the enzymes are protenious in nature. 
              

  Effect of PH :

  Like temperature, all enzymes have a optimum pH, at which the enzymatic activity will be at maximum. Many enzymes are most efficient in the region of pH 4-9 Outside this range, enzyme activity drops off very rapidly. If the relationship is plotted a typical bell-shaped curve will be obtained .

  Effect of enzyme concentration :

Enzyme concentration is directly proportional to the reaction velocity.  Rate of reaction steadily increases with the increases in enzyme concentration.  If graph is plotted between enzyme concentration and reaction velocity, linear relationship is obtained. 

 Effect of substrate Concentration :

 Reaction velocity of an enzymatic process increases with constant enzyme concentration and increase in substrate concentration. The velocity (V) is expressed in micromoles of substrate converted per minute.   As the concentration of substrate increases, the velocity of the reaction increases.  Continued increase in substrate concentration may lead to a reduction in rate of the reaction and leads to flattened curve.   The maximum velocity obtained from a enzymatic reaction is called as Vmax.  Vmax represents the maximum reaction rate possible in the presence of excess substrate. 

Presence of activators Presence of certain inorganic ions increases the activity of enzymes. The best examples are chloride ions activated salivary amylase and calcium activated lipases. 

  APPLICATION OF ENZYMES: 

1) Clinical application: 
 i. Lysozyme- It is used in the treatment of eye infection.
 ii. Trypsin- It is used in the treatment of acute ‘thrombophlebitis’(Blood clot and inflammation vein)
 iii. Streptokinase and urokinase- It is used in the treatment of thrombosis, embolism& it act as anticoagulant. 
iv. Pepsin, Renin-It is used in the treatment of gastric achylia.(undeveloped gastric gland)
 v. Fibrinolysin- It is used in the treatment of venous thrombosis, pulmonary & arterial embolism. 
vi. Asparginase-It is used in the treatment of some types of leukemia.
 vii. Penicillinase-It is usedin the treatment of persons who are allergic to penicillin. 

2) Medicinal application  :
 Sulphanilamide like drug act as antimetabolite is structurally similar with that of PABA which is required for the synthesis of folic acid competes with PABA &inhibit the enzyme folic acid synthetase, & thereby inhibitthe reaction of invading bacteria. With the help of competitive inhibitors like ephedrine, isoprenaline block the action of hormone adrenaline, noradrenaline & 5- HT can be prolonged by blocking the action of an enzyme monoamine oxidase which is responsible for the catabolism of these hormones. 
Xanthin oxidase enzyme is involved in the conversion of xanthin & hypoxanthin to uric acid.Allopurinol a competitive inhibitor of xanthin oxidase is used to reduce the conversion of xanthin &hypoxanthin to uric acid in the treatment of gout.

 3) Diagnostic Applications:
 Enzymes are very useful for the diagnostic of various diseases; most of the enzymes are present within the cell. The little amount of enzyme is present in body fluids like blood & C.S.F. etc. such enzymes are called ‘marker enzyme’. In disease condition level of these enzymes increases in blood or in other body fluids, hence we can easily identify the disease.

 i. The level of SGOT rises rapidly after a heart attack.
 ii. The level of SGPT increases in infectious hepatitis
 iii. Activity of Creatine-kinase increases in the plasma, during infection in cardiac muscle.

 4) Manufacturing Applications: 
 Enzymes are very useful for manufacturing of drugs e.g. 
• An enzyme ‘penicillin acylase’ is used for the production of 6-aminopenicillanic acid from Penicillin-G 
• For the preparation of digestants various enzymes like papain, pepsin, typsin are used.
 • Amylase is used in the production of dextrin.  Enzyme inhibition  Enzyme inhibition: These are agents or compounds which inactivate the enzymes, & thus adversely affect the rate of enzyme Catalyzedreaction is known as inhibitors & this whole process is known as enzyme inhibition.

Competitive inhibition:

In this type of inhibition structure of inhibitor (I) closely resembles with that of thesubstrate (S). The inhibitor thus competes with the substrate to combine with an enzyme (E) which formingthe enzyme inhibitor complex (EI) rather than (ES) complex.The degree of inhibitionare  depends upon the relative concentration of the substrate & theInhibitor. Thus by increasing the substrate concentration & keeping the inhibitor concentrationconstant the amount of inhibition get decreases & decrease in substrate concentration result in increasedenzyme inhibition. In this competitive inhibition, enzyme can either bind with substrate (ES) or inhibitor (EI)but not both. Vmax is unchanged KM is increased 

Noncompetitive Inhibition:

In this type of inhibition no competition occurs between the substrate (S) & the inhibitor (I). The inhibitor has littleor no structural resemblance with the substrate & it easily binds with an enzyme atthe  place other than active site. Thisbinding impairs the enzyme function. In this inhibition the inhibitor generally binds with enzyme as well asES complex. In this type of inhibition both EI & ESI complex formation take place. Vmax is lowered butKM value is unchanged 

ENZYMES : CLASSIFICATION, PROPERTIES, EFFECTS,TYPES,FACTORS
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Apniduniyas,

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