Non-enzymic oxidation of cysteinyldopa catalyzed by metallic ions.

1. Evidence is presented that under physiological conditions cysteinyldopa behaves similarly to catecholamines, e.g. adrenaline, in forming reversible complexes with various metallic cations. 2. As a rule, these complexes are stable under anaerobic conditions, but readily autoxidize in the presence of O2 to give the 1,4-benzothiazine acid (II) corresponding to one of the postulated intermediates in the biosynthesis of phaeomelanic pigments. 3. Copper catalyzed oxidation of cysteinyldopa proceeds differently to give the red-purple trichochrome F presumably via decarboxylation and oxidative coupling of the same benzothiazine intermediate. 4. The relevance of these in vitro experiments to the metabolism of cysteinyldopa is briefly discussed.