A Modified Dopa Reaction for the Diagnosis and Investigation of Pigment Cells

Three methods for a simple dopa (L-3,4-dmydroxyphenylalanine) reaction for frozen and paraffin-embedded sections and electron microscopy are presented. The classic methods were modified using fixatives and buffers currently used in enzyme histochemistry and electron microscopy. Cacodylate-buffered formaldehyde and glutaraldehyde proved to be excellent fixatives for light and electron microscopy dopa reactions, respectively. The sensitivity and specificity of the reaction were increased, replacing phosphate buffer with cacodylate buffer in the stock and working dopa solutions. These studies indicate that cacodylate buffer favors the enzymatic oxidation of dopa and interferes with its complete auto-oxidation. The three fractions of tyrosinase were demonstrated in human epidermal melanocytes, including the ribonucleoprotein-bound fraction, which had not been heretofore histochemically demonstrated.