The Secret Life of Levodopa
Levodopa is a therapeutic drug that is used to treat the symptoms of Parkinson’s disease. In the brain, this molecule is converted to the biochemically active dopamine by enzymatic decarboxylation. Dopamine is then used as a neurotransmitter to stimulate muscular movement. With its amine and carboxyl functional groups; Levodopa is also an amino acid but one that is not used in protein synthesis, sometimes called a non-protein amino acid. It is structurally very similar to Tyrosine and only differs by a single hydroxyl group. Levodopa enters the brain through an amino acid transporter. Levodopa is then taken up by specific neurones in the brain called dopaminergic neurones.
These specialized cells contain the enzyme AADC that converts DOPA to the neurotransmitter dopamine. However, in the neuron or any other cell, the similarity of levodopa to Tyrosine allows it to be mistakenly used to synthesize new proteins. This incorporation causes a change in the protein structure and in some cases the protein is no longer able to perform the correct role. It can even cause the protein to lose solubility In some cases these abnormal proteins can then be broken down and levodopa returned to the pool of amino acids to be used again. But some of the misfolded proteins are not degraded efficiently and begin to aggregate inside the cell. Some of these aggregates become resistant to being broken down and become insoluble plaques or tangles. This process can occur over many years or even decades. Eventually the buildup of these aggregates combined with other stress factors can cause the neurones to undergo apoptosis; a type of cell suicide.
Levodopa and Levodopa containing proteins can then be released into the surrounding environment where they can enter other cells leading to progressive neuronal death over time. This could have a negative impact on the sufferers brain function.
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