Pigmentation-associated
antigen (PAA) or gp75 is a
glycoprotein localized to the melanosomes of human
melanomas and melanocytes to which a mouse
monoclonal antibody (AbTA99) has been produced (T. M. Thomson et al. (1985) J. Invest. Dermatol. 85, 169). Treatment of 3H-labeled immunoprecipitated
melanoma PAA with alkaline-
borohydride, hydrazinolysis, or
N-glycanase released three families of
carbohydrate chains (I, II, and III). Peak I consists of a major component (Ia) of sialylated triantennary N-linked chains which are partially substituted with
fucose on terminal positions as well as on the
chitobiose core and a minor component (Ib) which is a sialylated biantennary N-linked species. Peak II was not well characterized but may be a monoantennary complex chain species. Peak III consists of typical N-linked high
mannose units with six to seven
mannose residues. Melanocyte PAA
carbohydrate chains have the same general features as
melanoma PAA except that the biantennary complex chain predominates; this difference resembles that observed between the cell surface
glycopeptides of transformed animal cells and their nontransformed counterparts. The glycosylation characteristics of this melanosomal
glycoprotein are compared with those of
glycoproteins from endoplasmic reticulum, Golgi, and lysosomes, and with
tyrosinase. It is suggested that the glycosylation pattern is a reflection of the biosynthetic origin and cellular destination of a particular organelle and its constituents.