Synthesis and Degradation of Catecholamines

Catecholamines  are:.

• Dopamine,Epinephrine, Norepinephrine
• Catecholamines  are compound  which contain Catecholnucleus.
• Site  of Synthesis: Chromaffin  cells of  Adrenal  Medulla and  Sympathetic  Ganglia.
•  In  adrenal  medulla major product is Epinephrine (80%).
• In organs  innervated  by  Sympathetic nerves  major product  is  Norepinephrine  (80%).

Conversion of Tyrosine  to  Epinephrine  involves  4 sequential  steps:

1.  Ring  Hydroxylation

2.  Decarboxylation

3.  Side  chain  hydroxylation

4.  N-Methylation.

• Tyrosine Hydroxylase  is  expressed only in  the  sites where  catecholamines are  synthesized,  where DOPA utilized  for  Catecholamine  synthesis.

lmportant  Points  Catecholamine  Synthesis

(A) Tyrosine Hydroxylase.

• Rate  limiting  step in  catecholamine  synthesis
• Similar  to  Phenylalanine  hydroxylase
• Monooxygenase.
• Require tetrahydrobiopterin.

(B) DOPA  Decarborylase

• Present  in  all  the  tissues
• PLP is  the  coenzyme  for  this  enzyme
• Degradation  of catecholamines.
• The  half life  of catecholamines  are very short, only 2-5  minutes. 

Degradation:

• Epinephrine  and  norepinephrine  is  catabolized  by Catechol  O Methyl Transferase (COMT)  then  by Monoamino Oxidase (MAO)
• The  major end product  of epinephrine  and norepinephrine is  Vanillyl Mandelic Acid( VMA).
• Normal level of VMA excretion in urine  is 2-4mg/2h hour.
• The major  end  product  of Dopamine  is  Homo Vanillic Acid  (HVA)

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