Question

Holoenzyme is the complete enzyme consisting of an apoenzyme and a cofactor. Select the option that correctly identifies the nature of apoenzyme and cofactor.
(a) Apoenzyme - Protein
      Cofactor - Non protein
(b) Apoenzyme - Non protein
      Cofactor - Protein
(c) Apoenzyme - Protein
      Cofactor - Protein
(d) None of these

Answer 1

Hint: Complex protein enzyme or conjugate enzyme, consists of a protein part, and a prosthetic group, coenzyme. Combination of apoenzyme with coenzyme constitutes the holoenzyme. Coenzyme is also known as cofactor.

Complete step by step answer:
- In 1878 the word ‘enzyme’ was initially used by the German physiologist Wilhelm Kühne, when he was describing the ability of yeast to produce alcohol from sugars.
- Enzymes possess remarkable specificity in that they generally catalyse the conversion of only one type or at most a range of similar types of substrate molecules into product molecules.
Principally enzymes are of three classes. They are:
Coenzyme:
- These are the enzymes that require some non- protein compounds known as co- factor in order to perform their catalytic activity.
- The binding or interaction between the apoenzyme and non- protein components is non- covalent, the small organic molecule is called a coenzyme.
- Coenzymes bind apoenzyme protein molecule to produce an active holoenzyme complex.
- Cofactors can be either inorganic like metal ions or organic compounds, like flavin and heme. Organic cofactors can be either prosthetic groups, which are tightly bound to an enzyme, or coenzymes, which are released from the enzyme's active site during the time reaction.
Apoenzyme:
- When enzymes do not possess the cofactor, the remaining conjugated proteins are called apoenzymes.
Holoenzyme:
- When enzymes possess chemical groups that are non- amino acids in nature, these conjugated proteins are called holoenzymes.
So, the correct answer is, Apoenzyme- Protein and Cofactor - Non protein.’

Note: Proenzyme or zymogen or precursor enzyme:
- Some proteolytic enzymes found in the blood or digestive tract are present in present in an inactive form precursor known as zymogen or proenzymes
- Some examples; prothrombin, proelastase, chymotrypsinogen, trypsinogen, pepsinogen which are produced and stored as inactive proenzyme or zymogen.