Bafilomycin A₁ inhibits the targeting of lysosomal acid hydrolases in cultured hepatocytes

Effects of bafilomycin A₁, an inhibitor of vacuolar H⁺-ATPase, on the synthesis and processing of cathepsin D and cathepsin H were investigated in primary cultured rat hepatocytes. Pulse-chase experiments showed that after being synthesized as procathepsin D and procathepsin H the precursors were converted into mature forms in the control cells as the chase time elapsed. However, in the presence of 5 × 10^-7 M of bafilomycin A₁, both precursors were largely secreted into the medium and no mature forms were found within the cells. Thus bafilomycin A₁ mimics lysosomotropic amines with regard to perturbation of the targeting of lysosomal acid hydrolases. In contrast, bafilomycin A₁ was found not to inhibit processings of proalbumin and procomplement component 3, which are thought to occur at the acidic trans-Golgi, implying that the proteolytic event of the proproteins is not sensitive to an increase of intra-Golgi pH. The results suggest that bafilomycin A₁ is useful as a pH-perturbant to study the role of acidity in living cells.