Intracellular distribution of dopa and 5-S-cysteinyldopa in Harding-Passey melanoma.

The concentrations of dopa and 5-S-cysteinyldopa were determined in the various cell fractions of Harding-Passey melanomas. Dopa was present in larger amounts than was 5-S-cysteinyldopa in all cell fractions, but the dopa/5-S-cysteinyldopa ratio was lower in the soluble fraction and in the small-granule fraction than in the large-granule fraction. The soluble fraction contained the greatest amount of catechols. These findings are compatible with high tyrosinase activity not only in the melanosomes but also in the small-granule and soluble fractions.