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 x 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.