Fig. 6. Characterization of an MT1-MMP- and furin-positive post-Golgi compartment in A375 melanoma cells by cryo-immuno-electron microscopy. MT1-MMP-transfected A375 cells were fixed and prepared for cryo-immunogold labeling as decribed in Materials and Methods by using differently sized gold particles, as indicated. Subcellular colocalization of MT1-MMP with endogenous furin: (A-C): 10 nm, anti-furin; 15 nm, anti-MT1-MMP (immunopurified antibody MMR2). Arrows mark the positions of specific regions containing both MT1-MMP and furin. Subcellular and plasma membrane colocalization of MT1-MMP with endogenous caveolin (D): 10 nm, anti-caveolin-1; 15 nm, anti-MT1-MMP (immunopurified antibody MMR2). PM indicates plasma membrane rims. C indicates caveosome. Bars, 100 nm (A); 75 nm (B,C); and 150 nm (D).