Cytochemical electron microscopy of cultured rat
hepatoma cells (AH-130) demonstrated that
thiamine pyrophosphatase (
TPPase) activity was localized in the Golgi complex. When the cells were treated with
brefeldin A (BFA, 2.5 micrograms/ml) for 10 min, the characteristic structure of the Golgi stack was no longer observed, and
TPPase was cytochemically stained in the vesicular and tubular structures scattered in the cytoplasm. A longer exposure of the cells to the
drug (20 min to 1 h) resulted in the distribution of the
TPPase activity in the endoplasmic reticulum (ER) and nuclear envelope. Such an unusual distribution of the
enzyme activity, however, was reversible even in the presence of BFA. At 2 h after the exposure, the
TPPase activity disappeared from the ER and was concentrated again in the vesicular and tubular structures. The
enzyme activity was finally localized in the Golgi complex which was reassembled by 4 h after the exposure. The reversible effect of BFA may be due to a possible metabolism of the
drug into an inert form during the incubation. Taken together, these results indicate that BFA causes a rapid disassembly of the Golgi complex and redistribution of the marker
enzyme TPPase into the ER including the nuclear envelope. The spontaneous reversibility of the
drug effect also favors a dynamic recycling of the Golgi marker between the ER and the Golgi complex under the conditions used.