AJP - Renal Physiology, Vol 252, Issue 5 890-F898, Copyright © 1987 by American Physiological Society
Subcellular distribution of renal tripeptide-releasing exopeptidases active on collagen-like sequences
K. J. Andersen and J. K. McDonald
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)
