Question:
Which of the following is a key enzyme involved in synthesis of phenolic compounds?
Which of the following is a key enzyme involved in synthesis of phenolic compounds?
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PAL activity in harvested fruits and vegetables is highly inducible by environmental stresses, mechanical wounding, and pathogen attacks, which explains why wounded plant tissues often synthesize and accumulate protective phenolic compounds (phytoalexins) rapidly.
Updated On: Aug 20, 2026
- Polyphenol oxidase
- Peroxidase
- Phenylalanine ammonia lyase
- Lipoxygenase
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The Correct Option is C
Solution and Explanation
Step 1: Understanding the Concept:
Phenolic compounds (flavonoids, tannins, lignins, and phenolic acids) are vital secondary metabolites in plants that contribute to food color, astringency, and antioxidant properties.
Their biosynthesis is regulated by specific enzymatic pathways.
Step 2: Detailed Explanation:
- Phenylalanine Ammonia-Lyase (PAL) is the first and most critical gateway enzyme of the phenylpropanoid pathway in plant tissues.
- It catalyzes the non-oxidative deamination of L-phenylalanine into trans-cinnamic acid, releasing ammonia.
- This reaction is the committed step that channels carbon from primary metabolism (shikimate pathway) into secondary metabolism for the synthesis of all plant phenolic compounds.
- Polyphenol oxidase and peroxidase are involved in the *degradation/oxidation* of phenolics (causing browning), not their synthesis.
- Lipoxygenase is involved in lipid oxidation.
Step 3: Final Answer:
The key enzyme involved in the synthesis of phenolics is Phenylalanine ammonia lyase, which corresponds to option (C).
Phenolic compounds (flavonoids, tannins, lignins, and phenolic acids) are vital secondary metabolites in plants that contribute to food color, astringency, and antioxidant properties.
Their biosynthesis is regulated by specific enzymatic pathways.
Step 2: Detailed Explanation:
- Phenylalanine Ammonia-Lyase (PAL) is the first and most critical gateway enzyme of the phenylpropanoid pathway in plant tissues.
- It catalyzes the non-oxidative deamination of L-phenylalanine into trans-cinnamic acid, releasing ammonia.
- This reaction is the committed step that channels carbon from primary metabolism (shikimate pathway) into secondary metabolism for the synthesis of all plant phenolic compounds.
- Polyphenol oxidase and peroxidase are involved in the *degradation/oxidation* of phenolics (causing browning), not their synthesis.
- Lipoxygenase is involved in lipid oxidation.
Step 3: Final Answer:
The key enzyme involved in the synthesis of phenolics is Phenylalanine ammonia lyase, which corresponds to option (C).
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