gamma-Glutamyl transpeptidase, tyrosinase, and 5-S-cysteinyldopa production in melanoma cells.

The distribution of gamma-glutamyl transpeptidase (gamma-GTP), tyrosinase, and 5-S-cysteinyldopa (5-S-CD) within melanoma cells has been studied in vitro as well as in vivo. Sodium periodate treatment of intact B-16 melanoma cells has been found to inhibit gamma-GTP present as an ectoenzyme. However, these periodate-treated cells in the presence of 10(-5) M dopa and glutathione have been found to continue to secrete large quantities of 5-S-CD in their medium. The large-granule fraction of Greene's melanotic melanoma contains substantial amounts of both tyrosinase and gamma-GTP. However, further separation of the large-granule fraction into sub-fractions indicates that tyrosinase and gamma-GTP seem to co-exist with premelanosome. It is suggested that glutathione-dependent t-S-CD genesis proceeds within premelanosomes through the formation of glutathione-dopa. The excess of glutathione-dopa and 5-S-CD, unutilized for pheomelanin formation overglow into the cytoplasm.