Cupric ions and DOPA oxidase activity in melanocytes

The inhibition of DOPA oxidase activity by cupric ions has been quantitated in cases of vitiligo showing dendritic and non-dendritic melanocytes at the margins. Cupric sulphate was added to the substrate solution, containing a reacting quantity of 12.12 micrograms of DOPA, to give 42.8 micrograms, 85.6 micrograms, 128.4 micrograms and 171.2 micrograms of cupric ions. Control slides were incubated with DOPA alone as substrate. On cytospectrophotometric analysis it was seen that the initial level of enzyme activity determines the type of inhibition curve. Thus, there is a gradual fall in activity with dendritic melanocytes which have a very high enzyme content, whereas the non-dendritic melanocytes show complete inhibition with one dose. It was observed that 15.75 micrograms of cupric ions were reduced by 12.12 micrograms of DOPA. The enzyme activation by cupreous ions is countered by the enzyme inhibition by cupric ions, the rate of inhibition being determined by the level of cupric ions.