False dopa reaction in studies of mammalian tyrosinase: some characteristics and precautions.

In cytochemical studies of B16 melanoma cells with the dopa reaction for tyrosinase, a false positive result that can easily be confused with authentic reactions has been observed. A preliminary characterization of this false reaction in comparison to authentic reactions with respect to stereospecificity, morphological characteristics, and subcellular localization has been conducted. Modifications of the classic dopa method have been devised that minimize occurrence of the false reaction.