Enzymes

Classifications of enzymes on the basis of their action on substrate

Oxidoreductases	Involved in oxidation-reductions Eg:-Phosphatase dehydrogenase, Alcohol dehydrogenase, Cytochrome oxidase
Transferases	Transfer of functional groups. Eg:- Hexokinase, Transaminase
Hydrolases	Hydrolysis reactions Eg:- Alkaline phosphatase, Lipase Carboxylic ester hydrolases
Lyases	Involved in addition or removal of water, ammonia, CO2,etc Eg:- Aldolase, Fumarase
Isomerases	Involved in isomerisation reactions Eg;- Phosphohexose isomerase, Epimerases
Ligases	Involved in synthetic reactions where 2 molecules are joined Eg :- Glutamine synthetase

1. Concentration of substrate increases within a limited range

2. Concentration of Enzyme directly proportional to the enzyme velocity of reaction

3. Temperature (increases to the maximum and then declines)

4. PH (increases to the maximum and then declines)

5. Product concentration
Accumulation of products generally decreases the enzyme velocity

6. Activators
Certain metal cations like Mn ,Mg ,Zn ,Ca ,Co ,Cu ,Na ,K affects enzyme activity.

7. Time
The longer the time, greater the amount of product but some might denature.

8. Light & radiation
Exposure to light and radiation might inactivate certain enzymes.

In competitive enzyme inhibition, Km is increased and Vmax is unchanged while in non – competitive inhibition, Km is unchanged and Vmax is decreased.

MCQs

a) Action on substrate
b) Action of coenzymes
c) Nature of the enzymes
d) All of the above

Answer A
Enzymes act mainly by lowering the activation energy of substrate.