5. Smith et al (1997)
Synthesis and degradation of
serotonin
Tryptophan
5-Hydroxytryptophan (5-
HTP)
Tryptophan hydroxylase
5-Hydroxytryptamine (5-
HT)
5-Hydroxytryptophan decarboxylase
5-Hydroxyindolacetic acid
(5-HIAA)
Monoamine oxidase (MAO)
6. Synthesis and degradation of
catecholamines
Phenylalanine
Key
COMT =
Catechol
O-methyltransferase
MAO =
Monoamine
oxidase
L-tyrosine
Dopamine
L-dopa
Tyrosine hydroxylase
3-methoxy-tyramine Noradrenaline3,4-dihydroxyphenylacetic acid
(DOPAC)
Homovalinillic
acid (HVA)
3-methoxy-4-hydroxy
phenylglycol (MHPG)
3-methoxy-4-hydroxy
mandelic acid (VMA))
COMT MAO MAO/COMT
Roth et al (1995)
7. Synthesis and degradation of
catecholamines
Phenylalanine
Key
COMT =
Catechol
O-methyltransferase
MAO =
Monoamine
oxidase
L-tyrosine
Dopamine
L-dopa
Tyrosine hydroxylase
3-methoxy-tyramine Noradrenaline3,4-dihydroxyphenylacetic acid
(DOPAC)
Homovalinillic
acid (HVA)
3-methoxy-4-hydroxy
phenylglycol (MHPG)
3-methoxy-4-hydroxy
mandelic acid (VMA))
COMT MAO MAO/COMT
Roth et al (1995)
Hinweis der Redaktion
Serotonin (5-HT) is an indolamine neurotransmitter synthesised from tryptophan, an essential amino acid found in the diet that is preferentially taken up by serotonergic neurons. The rate-limiting step in its formation involves tryptophan hydroxylase. 5-HT is catabolised by monoamine oxidase to form 5-hydroxyindolacetic acid.
·The rate-limiting step is between L-tyrosine and L-DOPA (tyrosine hydroxylase).
·The main break down products are MHPG, HVA and VMA.
·MAO acts mainly intraneuronally.
·COMT acts at the synaptic cleft.