Tissues 5-hydroxytryptophan decarboxylase

Dopa- and 5-hydroxytryptophane decarboxylase are probably identical. Both enzymes are similarly distributed in practically all tissues which have been examined, and the ratio of activity using dopa or 5-... 

The high affinity of the decarboxylase enzyme for its substrate (10 pM in the brain) makes it unlikely that this stage could ever become rate-limiting for the pathway as a whole. Nevertheless, the for this enzyme is considerably higher than tissue concentrations of 5-hydroxytryptophan and so, again, supply of this substrate is likely to be a crucial factor. 

Rahman, M. K Nagatsu, T., and Kato, T. (1981). Aromatic L-amino acid decarboxylase activity in central and peripheral tissues and serum of rats with L-DOPA and L-5-hydroxytryptophan as substrates. Biochem. Pharmacol. 30 645-649. 

The other physiologically important monoamine is 5-hydroxytryptamine (serotonin or 5-HT). It is formed from tryptophan via 5-hydroxytryptophan (5-HTP) Figure 5.2). The nature and properties of tryptophan-5-hydroxy-lase is still obscure, though the hydroxylation of tryptophan in vivo has been demonstrated. There is no clear evidence that this conversion occurs in brain tissue. The decarboxylation of 5-HTP, however, takes place in brain and the decarboxylating enzyme is found in all cerebral areas which contain 5-hydroxytryptamine. 5-HTP decarboxylase is closely related to, if not identical with, DOPA decarboxylase - and agents which inhibit dopan ine formation similarly inhibit the production of 5-hydroxytryptamine. There... 

Fig (2). Aromatic L-amino acid decarboxylase also known as tryptophan decarboxylase, catalyses the synthesis of 5-bydnoxyiriplaminc (serotonin) from 5-hydroxytryptophan. lire reaction consists of a decarboxylation activity that is found in many human tissue cells... 

The enzyme AADC is involved in different metabolic pathways synthesizing two important neurotransmitters dopamine and serotonin [24]. AADC decarboxylates L-dihydroxy-phenylalanine to form dopamine and 5-hydroxytryptophan to produce serotonin. Tryptophan decarboxylase activity is detected in many brain neurons and non-nervous tissue cells. 

Tissue Decarboxylase activity (5-hydroxytryptophane) Proportion of serotonin (msIs tissue) ... 

The specific action of serotonin, the amine produced by decarboxylation of 5-hydroxytryptophane, in stimulating cerebral activity, suggests that a specific decarboxylase for this substrate may be present in brain tissue. The amine itself cannot pass the so-C2illed blood-brain barrier, so must be formed in situ. A deficiency of serotonin results in mental depression. The serotonin produced by the kidney decarboxylase and carried in the blood may be concerned with control of blood pressure since it is a powerful vasoconstrictor. The two amines tyramine and tryptamine are both vasopressors. 

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