Immunofluorescent microscopy of cells stably expressing PZ. Cells were first cultured for 24 hours in the presence or the absence of vitamin K. After fixation and permeabilization, cells were incubated with a rabbit anti–human PZ antibody, followed by reaction with a FITC-labeled anti–rabbit IgG (top). The same cells were also stained with an anti-PDI monoclonal antibody coupled with a rhodamine-labeled anti–mouse IgG (bottom). Merged images are shown in the middle. Note that both the WT and Q30E PZs were detected in the Golgi apparatus only in the presence of vitamin K. Fluorescence was detected as described in the methods section (magnification × 40).