Phenylalanine Catabolism

• Phenylalanine catabolism is a crucial metabolic process that breaks down the amino acid phenylalanine into simpler compounds for use by the body.
• This process involves a series of biochemical reactions, primarily resulting in the production of tyrosine, which is further metabolized into substances that participate in key metabolic pathways.
• Main Steps in Phenylalanine Catabolism:

1. Conversion of Phenylalanine to Tyrosine:

   • Enzyme Involved: Phenylalanine hydroxylase (PAH)
   • Reaction: Phenylalanine is hydroxylated to form tyrosine.
   • Cofactors Required: Tetrahydrobiopterin (BH4) and oxygen.
   • Mechanism: PAH adds a hydroxyl group (-OH) to the benzene ring of phenylalanine, transforming it into tyrosine.

2. Tyrosine Catabolism:

   • Process: Tyrosine is further catabolized through several reactions.
   • Products: Fumarate and acetoacetate, which are utilized in the citric acid cycle and ketogenesis, respectively.

Metabolic Disorders of Phenylalanine Catabolism

• Disruptions in the normal catabolism of phenylalanine can lead to metabolic disorders, the most notable of which is Phenylketonuria (PKU).

  • Phenylketonuria (PKU):

    • Cause: Deficiency in the enzyme phenylalanine hydroxylase (PAH) or its cofactor, tetrahydrobiopterin (BH4).
    • Consequences: Accumulation of phenylalanine and its toxic metabolites in the body.
    • Symptoms: Intellectual disability, developmental delays, and other neurological symptoms if not managed with a diet low in phenylalanine.
    • Variants: Ranges from classic PKU with severe PAH deficiency to milder forms such as hyperphenylalaninemia.

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