Background: During melanogenesis, the activity of tyrosinase (the key enzyme for melanin synthesis) is important in the diagnosis of melanomas. Methods: Nine samples were included in this study, based on the availability of four malignant melanomas and five benign tumours. Our new approach is based on a combination of the DOPA oxidase and the glyoxylic acid (GA) methods for catecholamine (named the ‘DOPA-GA method’). Here, we compared the conventional DOPA oxidase method with that of the DOPA-GA method. Results: In all malignant melanomas, the fluorescence intensity of the DOPA-GA method was strongly expressed within the cytoplasm. The melanoma cells showed an obvious sensitivity compared with the Laidlaw and Blackberg method, as did the melanocytes in the normal skin. Detection was easier with the DOPA-GA method than the Laidlaw and Blackberg method. Hence, we developed a sensitive and rapid method with a total assay time of less than 30 min. Conclusion: DOPA-GA reflects tyrosinase activity in melanocytic tumours, and our new approach is an improvement on the conventional DOPA oxidase method, with regard to both specificity and sensitivity. The DOPA-GA method will be useful for routine pathological testing and melanogenetic studies of melanocytes and melanocytic tumours.

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