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.