Metabolism of Aromatic Amino Acids

Acetoacetate is a primary ketone body. Beta hydroxy butyrate and acetone are secondary ketone bodies. Acetoacetate can be formed from acetyl CoA, it can also be formed by the degradation of carbon skeleton of ketogenic amino acids like leucine, lysine, phenylalanine and tyrosine.

Amino acids and products

• Cysteine forms glutathione, taurine etc.
• Histidine forms histamine
• Tryptophan forms serotonin, melatonin etc.
• Under normal circumstances, the degradation of phenylalanine mostly occurs through tyrosine. Phenylalanine is hydroxylated at para-position by phenylalanine hydroxylase to produce tyrosine (p-hydroxy phenylalanine)

Individuals living with PKU must keep their intake of phenylalanine extremely low to prevent mental retardation and other metabolic complications.

However, phenylalanine is the precursor for tyrosine synthesis.

Without phenylalanine, tyrosine cannot be made and so tyrosine becomes essential in the diet of PKU patients.

Ans. is ‘b’ i.e., Insulin

Ans. is ‘c’ i.e., Melanin

Tyrosine is a precursor of many important compounds such as catecholamines (epinephrine, norepinephrine ), dopamine), thyroxine, triiodothryonine, melanin.

Tyrosinemia

It is a defect in metabolism of tyrosine. It may be of following types :-

1. Tyrosinemia type-I (tyrosinosis/hepatorenal syndrome) :- It is due to defect in fumarylacetoacetate hydroxylase deficiency. Patients with chronic tyrosinosis are prone to develop cirrhosis and hepatic carcinoma. There is cabbage like odor in acute tyrosinosis.
2. Tyrosinemia type – II (Richer-Hanhart syndrome) :- It is due to deficiency of tyrosine transaminase (tyrosine aminotrans-ferase).
3. Neonatal tyrosinemia : – It is due to deficiency of hydroxyphenyl pyruvate hydroxylase.

Ans. is ‘b’ i.e., Tyrosine 

• Catecholamines (epinephrine, norepinephrine and dopamine) are synthesized from tyrosin.
• Has been explained in previous seesions.