Association of cell surface receptors for melanotropin with the Golgi region in mouse melanoma cells.

Binding of beta-melanotropin (betal-melanocyte stimulating hormone) to mouse melanoma cells occurs in a region on the cell surface overlying the Golgi complex. This association was demonstrated by labeling cells with fluorescein isothiocyanate hormone and by locating the Golgi complex with a histochemical test for thiamine pyrophosphatase activity. The biologically active fluorescent hormone appears on the surface and later in vesicles in the malanized cells, as judged by fluorescence microscopy. It is conceivable that internalization of the hormone is instrumental in the process of hormonally induced melanization. Because initial and late events of hormonally induced pigmentation are related to the Golgi complex, it is likely that instructions that follow the attachment of melanotropin to receptors are carried out in a compartmentalized manner.