Intracellular transport and processing of lysosomal cathepsin B

Intracellular transport and processing of lysosomal cathepsin B was investigated in the subcellular fractions of rat liver by pulse-labeling experiments with 35S]methionine in vivo. A newly synthesized procathepsin B with a molecular weight of 39 kDa firstly appeared in the rough microsomal fraction at 10 min postinjection of label. This procathepsin B moved from the microsomal fractions to the Golgi subfractions at 30 min postinjection, and then a processed mature enzyme appeared in the lysosomal fraction at 60 min. These results suggest that the propeptide-processing of procathepsin B takes place in lysosomes in the course of intracellular transport from endoplasmic reticulum through Golgi complex to lysosomes.