Scheme 1.

Schematic illustration of the polypeptide chain of PPO4 mushroom tyrosinase. The polypeptide chain of active tyrosinase (core-region) is colored in red. It ranges from Ser² to the determined cleavage site at Ser³⁸³. This A-TYR part contains both copper binding sites forming the active site as well as the thioether bridge between Cys⁸⁰ to His⁸². The C-terminal part is colored in orange. It starts with position Glu³⁸⁴ and ends with the cleavage site at Thr⁵⁶⁵. The untraceable C-terminal tail above Thr⁵⁶⁵ is colored purple. Amino acids of this part were not found during this investigation. Computer based structure modeling of this sequence tail suggests the presence of a trans-membrane helix between Ala⁵⁶⁹ and Ala⁵⁹¹. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)