L-DOPA, also known as levodopa or 3,4-dihydroxyphenylalanine is an alpha amino acid. These are amino acids in which the amino group is attached to the carbon atom immediately adjacent to the carboxylate group (alpha carbon).  L-DOPA is found naturally in both animals and plants. It is made via biosynthesis from the amino acid L-tyrosine by the enzyme tyrosine hydroxylase.. L-DOPA is the precursor to the neurotransmitters dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline), which are collectively known as catecholamines. The Swedish scientist Arvid Carlsson first showed in the 1950s that administering L-DOPA to animals with drug-induced (reserpine) Parkinsonian symptoms caused a reduction in the intensity of the animals' symptoms. Unlike dopamine itself, L-DOPA can be taken orally and crosses the blood-brain barrier. It is rapidly taken up by dopaminergic neurons and converted to dopamine. In particular, it is metabolized to dopamine by aromatic L-amino acid decarboxylase. Pyridoxal phosphate (vitamin B6) is a required cofactor for this decarboxylation, and may be administered along with levodopa, usually as pyridoxine. As a result, L-DOPA is a drug that is now used for the treatment of Parkinsonian disorders and DOPA-Responsive Dystonia. It is usually given with agents that inhibit its conversion to dopamine outside of the central nervous system. It is standard clinical practice in treating Parkinsonism to co-administer a peripheral DOPA decarboxylase inhibitor - carbidopa or benserazide - and often a catechol-O-methyl transferase (COMT) inhibitor, to prevent synthesis of dopamine in peripheral tissue. Side effects of L-DOPA treatment may include: hypertension, arrhythmias, nausea, gastrointestinal bleeding, disturbed respiration, hair loss, disorientation and confusion. L-DOPA can act as an L-tyrosine mimetic and be incorporated into proteins by mammalian cells in place of L-tyrosine, generating protease-resistant and aggregate-prone proteins in vitro and may contribute to neurotoxicity with chronic L-DOPA administration. L-phenylalanine, L-tyrosine, and L-DOPA are all precursors to the biological pigment melanin. The enzyme tyrosinase catalyzes the oxidation of L-DOPA to the reactive intermediate dopaquinone, which reacts further, eventually leading to melanin oligomers.