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l-DOPA can be manufactured and in its pure form is sold as a drug with the INN Tooltip International Nonproprietary Name levodopa. Trade names include Sinemet, Pharmacopa, Atamet, and Stalevo. As a drug, it is used in the clinical treatment of Parkinson's disease and dopamine-responsive dystonia. l-DOPA has a counterpart with opposite chirality ...
Levodopa crosses the protective blood–brain barrier, whereas dopamine itself cannot. [3] [4] Thus, levodopa is used to increase dopamine concentrations in the treatment of Parkinson's disease, Parkinsonism, dopamine-responsive dystonia and Parkinson-plus syndrome. The therapeutic efficacy is different for different kinds of symptoms.
In dopaminergic cells in the brain, tyrosine is converted to L-DOPA by the enzyme tyrosine hydroxylase (TH). TH is the rate-limiting enzyme involved in the synthesis of the neurotransmitter dopamine. Dopamine can then be converted into other catecholamines, such as norepinephrine (noradrenaline) and epinephrine (adrenaline).
d-DOPA (D-3,4-dihydroxyphenylalanine; dextrodopa) is similar to L-DOPA (levodopa), but with opposite chirality. Levo - and dextro - rotation refer to a molecule's ability to rotate planes of polarized light in one or the other direction.
In the second stage L-DOPA (levodopa) is formed by adding a phenol group to the benzene ring of L-tyrosine. The formation of L-DOPA from L-tyrosine is catalyzed by the enzyme tyrosine hydroxylase. The third stage is the formation of dopamine by removing the carboxylic acid group from L-DOPA, catalysed by the enzyme dopa decarboxylase. [31]
The enzyme tyrosine hydroxylase (TH) converts the amino acid L-tyrosine into 3,4-dihydroxyphenylalanine (L-DOPA). The hydroxylation of L-tyrosine by TH results in the formation of the DA precursor L-DOPA, which is metabolized by aromatic L-amino acid decarboxylase (AADC; see Cooper et al., 2002 [citation needed]) to the transmitter dopamine ...