Thermal activation and inactivation of melanin formation in vertebrate skins and melanomas.

The melanogenic activity of tyrosinase as a function of temperature was studied in 9 different skin and melanoma tissues of vertebrates. The 600 times g supernatant fraction of tissue homogenates was incubated with 14C-L-tyrosine at 0 degrees to 60 degrees C for 16 hr and the 14C-melanin product was determined. The range of optimal temperature occurred at 35 degrees to 45 degrees C. The maximal activity and thermostability depended on the source of the enzyme preparation utilized. Thermal activation and species differences in the optimal temperature for maximal activity are complicated processes which depend upon many factors. At cold conditions, a higher percentage of maximal activity was achieved with enzyme from cold-blooded species than with enzyme from warm-blooded species.