title: [Intracellular protein breakdown. VIII. The use of double-labeled proteins as substrates].
abstract: Double-labeled proteins from rat liver cytosol (14C in long-lived, 3H in short-lived proteins after in-vivo-labeling) are used as substrates for unlabeled proteinases in vitro. Differences in the degradation rates of short-lived and long-lived proteins in vitro by different proteinases and after addition of different effectors allow conclusions concerning their importance for the in-vivo-turnover of substrate proteins. The main activity (greater than 90%) of soluble-lysosomal proteinases at pH 6,1 and pH 6,9 is caused by thiolproteinases, which degrade preferentially short-lived cytosol proteins. These proteinases are inhibited by leupeptin. Autolysis of double-labeled cell fractions shows a remarkably faster breakdown of short-lived substrate proteins only in the soluble part of lysosomes. Microsomal fractions degrade in vitro preferentially long-lived substrate proteins.
mesh_terms: D000818:Animals; D002250:Carbon Radioisotopes; D003600:Cytosol / Q000201:enzymology; D007553:Isotope Labeling; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008297:Male; D010447:Peptide Hydrolases / Q000378:metabolism*; D051381:Rats; D013329:Structure-Activity Relationship; D013347:Subcellular Fractions / Q000201:enzymology; D014316:Tritium
chemical_list: D002250:Carbon Radioisotopes; D014316:Tritium; D010447:Peptide Hydrolases
vernacular_title: Intrazellulärer Proteinabbau. VIII. Einsatz doppeltmarkierter Substrarproteine