Question

Apoenzyme is a
A. Protein
B. Carbohydrate
C. Vitamin
D. Amino acid

Answer 1

An enzyme is a biochemical formed in our body that enables a biochemical reaction to being catalyzed. With the exception of ribozymes, it is primarily protein.

Complete answer:
Apoenzyme is a protein in the body. When an organic or inorganic molecule known as a cofactor is bound together with the enzyme, the enzyme is activated. For instance, the 'pyruvate dehydrogenase' enzyme has five cofactors, namely $TPP,\text{ }FA{{D}^{+}},\text{ }NAD,\text{ }CIA$ and magnesium. Apoenzyme, along with its cofactor, is known as 'Holoenzyme.' Cofactor' is a non-protein molecule that allows the apoenzyme to create a metabolic reaction.
Organic cofactor forms are:
Organic cofactors-Examples: Vitamin ${{B}_{3}}$, Flavin, ATP, etc.
Inorganic cofactors or Minerals-Examples: Zn is a cofactor of Alcohol dehydrogenase and Carbonic Anhydrase, Nickel is a cofactor of Urease, Copper is a cofactor of Cytochrome oxidase.
Organic cofactors are further classified into two groups-
Coenzyme-These remains loosely bound to the enzyme.
Prosthetic group-T-Organic cofactors.
Apoenzyme is a protein portion of a holoenzyme that becomes inactive when isolated from its cofactor or prosthetic unit. An active holoenzyme is then formed by the apoenzyme and the cofactor/prosthetic group together. The holoenzyme cofactor is a non-protein component and is responsible for the function of the enzyme.

So, choice A- Protein is the correct answer.

Note: The inactive form of the apoenzyme is known as a proenzyme or a zymogen. In the protein structure, the proenzyme can contain several extra amino acids that are removed, leading to the formation of a final unique tertiary structure before it is activated as an apoenzyme.