Question:
The Old Yellow Enzyme (OYE), isolated by Warburg and Christian from brewers' bottom yeast in 1932, has been shown to comprise of a colourless apoprotein and a yellow cofactor. Subsequent identification of the nature of this yellow cofactor demonstrated that OYE is a(an):
The Old Yellow Enzyme (OYE), isolated by Warburg and Christian from brewers' bottom yeast in 1932, has been shown to comprise of a colourless apoprotein and a yellow cofactor. Subsequent identification of the nature of this yellow cofactor demonstrated that OYE is a(an):
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Flavin cofactors (FMN and FAD) can undergo both one-electron transfers (forming a stable semiquinone radical intermediate) and two-electron transfers, making them versatile adaptors between two-electron obligate donors and one-electron acceptors.
Updated On: Jul 23, 2026
- Ribozyme
- Flavoenzyme
- Metalloenzyme
- Abzyme
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
Enzymes often require non-protein chemical components called cofactors to catalyze biochemical reactions.
A holoenzyme is composed of a protein portion (apoprotein) and a tightly or covalently bound organic cofactor (prosthetic group) or coenzyme.
Step 2: Detailed Explanation:
The Old Yellow Enzyme (OYE) was the first conjugated protein enzyme to be isolated and purified, marking a milestone in the history of biochemistry.
Otto Warburg and Walter Christian isolated it from yeast and observed that the active enzyme had a distinct yellow color, which was lost upon separating the protein from its non-protein cofactor.
Subsequent structural and chemical analysis of this yellow cofactor identified it as riboflavin-5'-phosphate, commonly known as flavin mononucleotide (FMN).
FMN is a derivative of riboflavin (Vitamin B2), which is naturally yellow due to the conjugated isoalloxazine ring system.
Enzymes that contain FMN or flavin adenine dinucleotide (FAD) as prosthetic groups are classified as flavoenzymes (or flavoproteins).
They play central roles in oxidation-reduction reactions by catalyzing the transfer of one or two electrons.
Therefore, the characterization of the yellow cofactor established that OYE is a flavoenzyme.
The other options are incorrect: ribozymes are catalytic RNA molecules, metalloenzymes require metal ions for activity, and abzymes are catalytic antibodies.
Step 3: Final Answer:
The Old Yellow Enzyme is a flavoenzyme, corresponding to option (B).
Enzymes often require non-protein chemical components called cofactors to catalyze biochemical reactions.
A holoenzyme is composed of a protein portion (apoprotein) and a tightly or covalently bound organic cofactor (prosthetic group) or coenzyme.
Step 2: Detailed Explanation:
The Old Yellow Enzyme (OYE) was the first conjugated protein enzyme to be isolated and purified, marking a milestone in the history of biochemistry.
Otto Warburg and Walter Christian isolated it from yeast and observed that the active enzyme had a distinct yellow color, which was lost upon separating the protein from its non-protein cofactor.
Subsequent structural and chemical analysis of this yellow cofactor identified it as riboflavin-5'-phosphate, commonly known as flavin mononucleotide (FMN).
FMN is a derivative of riboflavin (Vitamin B2), which is naturally yellow due to the conjugated isoalloxazine ring system.
Enzymes that contain FMN or flavin adenine dinucleotide (FAD) as prosthetic groups are classified as flavoenzymes (or flavoproteins).
They play central roles in oxidation-reduction reactions by catalyzing the transfer of one or two electrons.
Therefore, the characterization of the yellow cofactor established that OYE is a flavoenzyme.
The other options are incorrect: ribozymes are catalytic RNA molecules, metalloenzymes require metal ions for activity, and abzymes are catalytic antibodies.
Step 3: Final Answer:
The Old Yellow Enzyme is a flavoenzyme, corresponding to option (B).
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