title: Subcellular distribution of renal tripeptide-releasing exopeptidases active on collagen-like sequences.
abstract: The rat kidney cortex was found to contain two N-terminal exopeptidases of the tripeptidyl peptidase (TPP) class. Each required a free N-terminus to catalyze the release of collagen-related (Gly-Pro-X) "triplets." In accordance with their apparent pH optima, activities were routinely determined fluorimetrically at pH 4.0 (TPP 4) and at pH 7.0 (TPP 7) on Gly-Pro-Met-2-naphthylamide. The specific activity in both the homogenate and the classical subfractions was much greater at pH 7 than at pH 4. Subfractionation of the microsomal fraction by equilibrium banding in sucrose did not separate the TPP 4 and TPP 7 activities. The banding density (1.18 g/ml) and the distribution patterns for TPP 7 in the microsomal subfractions, and also in the subfractions of the small lysosomes in the mitochondrial-lysosomal (ML) fraction, demonstrate that TPP 7 is associated with smooth membranes. The TPP 4 and TPP 7 activities were clearly separated during subfractionation of the ML fraction. Rate sedimentation demonstrated that TPP 4 was present in the large, fast-sedimenting lysosomes (protein droplets) and in a heterogeneous broad band of smaller lysosomes. Equilibrium banding of the small lysosomes gave two distinct TPP 4-containing populations at densities 1.20 and 1.235 g/ml. Notably, dipeptidyl peptidase II (DPP II) gave identical banding densities and showed distributions very similar to TPP 4.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000626:Aminopeptidases; D000818:Animals; D003094:Collagen / Q000378:metabolism*; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; D010450:Endopeptidases / Q000145:classification / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000201:enzymology* / Q000378:metabolism / Q000648:ultrastructure; D007672:Kidney Cortex / Q000201:enzymology; D008081:Liposomes / Q000378:metabolism; D008297:Male; D009940:Organoids / Q000201:enzymology; D051381:Rats; D011919:Rats, Inbred Strains; D013347:Subcellular Fractions / Q000201:enzymology; D014018:Tissue Distribution
chemical_list: D008081:Liposomes; D003094:Collagen; D010450:Endopeptidases; D000626:Aminopeptidases; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases