Metabolism of leupeptin and its effect on autophagy in the perfused rat liver

Metabolism of the potent, thiol proteinase inhibitor, leupeptin, was studied in the perfused rat liver. This bacterial peptide (2.5 mg) caused the lysosomes to become enlarged and filled with electron-dense material. The subcellular distribution of the lysosomal enzyme, beta-D-hexosaminidase, was altered, the major change being a 50% loss of its activity from the L-fraction of the homogenate. The enzyme became redistributed in the other homogenate fractions. The density of the leupeptin-formed lysosomes compared to normal organelles was increased from 1.206 to 1.230 g/ml. Radioactive [3H]leupeptin was slowly taken up by a perfused liver (approximately 0.06 mumole/h/g liver) and almost immediately appeared in the bile in a form still capable of inhibiting papain. Liver radioactivity was concentrated in both the lysosomal (39%) and soluble fractions (38%) of the tissue homogenate.