Involvement of tyrosinase in melanin formation in murine melanoma.

The possibility that peroxidase is functional in melanogenesis in the murine S-91 melanoma has been investigated. It was found that, as in the normal mouse, tyrosinase is the enzyme responsible for the bulk of melanin formation in the malignant melanocyte. Tyrosinase was capable of utilizing tyrosine as a substrate, as well as dopa, although the Vmax with dopa was much higher than with tyrosine. Conversely, the affinity of the enzyme for tyrosine is higher than for dopa, and this relationship may in part be responsible for the occasional misinterpretation of the functional capability of this enzyme.