Dopa oxidase activity in human hair bulbs measured by high-performance liquid chromatography

A method for measuring the dopa oxidase (DO) activity of human hair bulb tyrosinase has been developed and the results of this method have been compared with the tyrosine hydroxylase (TH) activity of hair bulb tyrosinase for brown-, black-, blond-, and red-haired subjects. The method takes advantage of the rapid trapping of dopaquinone by cysteine with the subsequent formation of cysteinyldopas which can be measured by high-performance liquid chromatography. 5-S-Cysteinyldopa (5SCD) and 2-S-cysteinyldopa (2SCD) were detected in the reaction products. Formation of 5SCD correlated with the TH activity over the full range of hair colors and enzyme activity, while 2SCD appeared to be formed nonenzymatically. The absolute amount of 2SCD was constant for each individual but did not correlate with hair color or TH activity. The formation of 5SCD was linear for 60 min while most of the 2SCD was formed within seconds and did not change with time. White hair bulbs which demonstrated no TH activity formed 2SCD, but not 5SCD. We conclude that tyrosinase activity can be quantitated in human hair bulbs by this method, and that TH and DO are coordinate functions of tyrosinase over a broad range of hair color and enzyme activity.