Tyrosinase in Melanized Melanosomes

The effect of melanization on the tyrosinase and acid phosphatase of melanosomes isolated from Harding-Passey mouse melanomas was studied. Inactivation effect was clearly shown in both tyrosinase activity and acid phosphatase activity to be due to melanization. The melanosomes melanized in vitro and in vivo were treated with deoxycholate, and subjected to sonication and trypsin digestion. No significant tyrosinase activity was released from these melanosomes by such treatment. Therefore, the blocking processes of the active center in tyrosinase are assumed to be very tight and impossible to remove easily. The inactivation process of tyrosinase might be irreversible during melanization of melanosomes. Under the scanning electron microscope melanosomes appear to be covered unevenly by amorpous masses during melanization.