Neuromelanin formation. The initial precursor is L-tyrosine, which is hydroxylated to L-dopa by neuronal tyrosine hydroxylase. The high amino acid decarboxylase activity in catecholaminergic neurons yields dopamine and this is oxidized to dopaminequinone. This reaction might be catalyzed by a peroxidase or it occurs spontaneously by the action of oxygen reactive species. Similarly to L-dopaquinone in the Raper-Mason pathway, this quinone is pivotal in the route, giving place to 5-S-cysdopamine or DHI depending on the presence or the absence of L-cys during the dopaminequinone formation. Neuromelanin is usually a mixed melanin, as both indole and benzothiazine units are incorporated to its structure.