Question

Define in detail the differences between apoenzyme, holoenzyme, cofactor, coenzyme and transition state and how the presence or absence of above factors effect enzyme activity

Answer 1

Apoenzyme:

• An apoenzyme is an inactive, incomplete part of an enzyme which undergoes activation after binding within organic coenzyme or an inorganic cofactor.

Holoenzyme:

• This is the complete enzyme containing both apoenzyme and the coenzyme/cofactor.

• Holoenzyme is the activated form.

Cofactor:

• This is an inorganic ion or element which binds with the apoenzyme and makes it active.

• Examples: Cu+2 (cupric ion) in Alcohol dehydrogenase enzyme.

Coenzyme:

• These are organic substances attached to the apoenzyme in order to activate them.

• The common co-enzymes are Vitamin B3 (nicotinamide) , Vitamin B2 (FAD) , etc.

Transition state:

• It is highest energy state in an enzyme mediated reaction, which marks the activation energy.

• Once activation energy is reached, the transition state is overcome it and product formation begins.

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