5-S-Cysteinyldopa in ganglion stellatum

5-S-Cysteinyldopa, an amino acid formed by nucleophilic addition of cysteine to dopaquinone, has been detected in the ganglion stellatum of the cow in amounts varying between 21 and 35 ng/g ganglionic tissue. Dopa was present in slightly higher quantities. Cysteinyldopa has previously been regarded as a substance unique for the melanocytes, where it forms melanin after oxidation and polymerization. At present only hypothetical explanations of our finding can be offered. The content of 5-S-cysteinyldopa in ganglion stellatum may be the result of dopa oxidation in ganglionic cells. An uptake mechanism for circulating cysteinyldopa may exist. Localization of cysteinyldopa to aberrant melanocytes or to aged SIF-cells in the ganglia should also be borne in mind.