SUBCELLULAR-LOCALIZATION AND FUNCTION OF MELANOGENIC ENZYMES IN THE INK GLAND OF SEPIA-OFFICINALIS

The ink gland of the cuttlefish Sepia officinalis has traditionally be en regarded as a convenient model system for investigating melanogenes is. This gland has been shown to contain a variety of melanogenic enzy mes including tyrosinase, a dopachrome-rearranging enzyme and peroxida se. However, whether and to what extent these enzymes co-localize in t he melanogenic compartments and interact is an open question. Using po lyclonal antibodies that recognize the corresponding Sepia proteins, w e have been able to demonstrate that peroxidase has a different subcel lular localization pattern from tyrosinase and dopachrome-rearranging enzyme. Whereas peroxidase is located in the rough endoplasmic reticul um and in the matrix of premelanosomes and melanosomes, tyrosinase and dopachrome-rearranging enzyme are present in the rough endoplasmic re ticulum-Golgi transport system, at the level of trans-Golgi cisternae, trans-Golgi network and coated vesicles, and in melanosomes on pigmen ted granules. These results fill a longstanding gap in our knowledge o f the melanin-producing system in Sepia and provide the necessary back ground for dissection at the molecular level of the complex interactio n between melanogenic enzymes. Moreover, the peculiar and complex orga nization of melanin in an invertebrate such as Sepia officinalis is su rprising and could provide the basis for understanding the process in more evolved systems such as that of mammals.