Intracellular transport and processing of lysosomal cathepsin H.

Intracellular transport and processing of lysosomal cathepsin H was investigated in the subcellular fractions of rat liver by pulse-labeling experiments with [35S]methionine in vivo. A newly synthesized procathepsin H with a molecular weight of 41 kDa first appeared in the rough microsomal fraction at 10 min postinjection of label. This procathepsin H moved from the microsomal fraction to the Golgi subfractions at 30 min. Then a processed single-chain form with 28 kDa appeared in the lysosomal fraction at 60 min and persisted as the predominant form after 180 min. These results suggest that the propeptide-processing of procathepsin H indeed takes place in lysosomes in the course of intracellular transport from endoplasmic reticulum via Golgi complex to lysosomes.