Inhibitions of cathepsin B and cathepsin L by E-64 in vivo. II. Incorporation of [3H]E-64 into rat liver lysosomes in vivo.
E-64 is a specific thiol proteinase inhibitor which inhibits lysosomal cathepsins B and L in vitro and in vivo [Hashida, S., Towatari, T., Kominami, E., & Katunuma, N. (1980) J. Biochem. 88, 1805-1811]. This work showed and that E-64 administered in vivo penetrates into lysosomes of the liver, possibly by permeation rather than by endocytosis. When [3H]E-64 was injected into rats i.p., high radioactivity was observed in the serum after a short time and it decreased rapidly. Incorporation of [3H]E-64 into the cytosol fraction of liver also began to decrease 1 h after the injection. Radioactivity in the mitochondrial-lysosomal fraction increased to a maximum after 6 h and then gradually decreased until 72 h. Dose-dependent incorporation of [3H]E-64 into the serum and liver cytosol was observed at all doses tested, but that into the lysosomal fraction increased linearly with doses of only up to 0.l5 mg/100 body weight of E-64. E-64 in the serum and liver cytosol was mostly present in the free form, whereas that in the lysosomal fraction was mostly protein-bound. The time course and dose-response of lysosomal cathepsin B activity to E-64 were closely related to the radioactivity in the protein-bound fraction of the lysosomes. These results suggest that E-64 was transported to the liver cytosol in the free form in the blood and permeated into the lysosomes, where it bound to, and inactivated, E-64 sensitive proteinases.
D000818:Animals; D002401:Cathepsin B; D056668:Cathepsin L; D002403:Cathepsins / Q000037:antagonists & inhibitors*; D003546:Cysteine Endopeptidases; D010450:Endopeptidases; D066298:In Vitro Techniques; D007930:Leucine / Q000031:analogs & derivatives* / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism*; D008297:Male; D011485:Protein Binding; D051381:Rats; D011919:Rats, Inbred Strains; D013347:Subcellular Fractions / Q000378:metabolism; D013997:Time Factors
D002403:Cathepsins; D010450:Endopeptidases; D003546:Cysteine Endopeptidases; D002401:Cathepsin B; D056668:Cathepsin L; C534280:Ctsl protein, rat; D007930:Leucine; C024974:E 64