Acetate Pathway (Polyketide Pathway)

Overview of Acetate Pathway (Polyketide Pathways):

• The Acetate pathway, often referred to as the polyketide pathway, involves the polymerization of acetyl-CoA or malonyl-CoA units.
• It is crucial not only for primary metabolites like fatty acids but also for numerous plant secondary metabolites (e.g., flavonoids, certain antibiotics in microorganisms, and various phenolics in plants).

Key Steps:

1. Acetyl-CoA Generation

   • Acetyl-CoA is produced from:
     • Glycolysis: Through the pyruvate dehydrogenase complex.
     • Fatty acid β-oxidation.
   • Malonyl-CoA is formed from acetyl-CoA by the enzyme acetyl-CoA carboxylase.

2. Polyketide Chain Elongation

   • The acetate (acetyl-CoA) or malonate (malonyl-CoA) units undergo condensation reactions to form polyketide chains.
   • Malonyl-CoA donates two-carbon units to elongate the chain.
   • These steps are catalyzed by polyketide synthases (PKSs).

3. Cyclization and Modification

   • The linear polyketide chains undergo various modifications, including:
     • Cyclization: Formation of phenolic or aromatic ring structures.
     • Reduction, Oxidation, Methylation: Generate diverse molecular scaffolds.
   • These modifications create the structural diversity seen in polyketide-derived compounds.

Major Secondary Metabolites from the Acetate/Polyketide Pathway:

1. Fatty Acids: Membrane components (primary metabolism).
2. Flavonoids: Pigments, antioxidants (linked to Shikimic pathway).
3. Quinones: E.g., anthraquinones.
4. Tannins: Derived from gallic acid.
5. Phenolics: Polyketide-based compounds.

Biological Significance:

1. Structural Protection: Waxes and cutin from fatty acids form protective barriers on leaves and fruits.
2. Defense: Polyketide-derived phytoalexins, tannins, and flavonoids deter herbivores and pathogens.
3. Pigmentation: Flavonoids and anthraquinones enhance flower and fruit coloration, attracting pollinators.

Applications:

• Agriculture: Waxes and cutin for protective coatings.
• Pharmaceuticals: Polyketides as precursors for antibiotics (e.g., erythromycin) and anticancer drugs.
• Biotechnology: Engineering polyketide pathways for industrial use.

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