AJP - Gastrointestinal and Liver Physiology, Vol 250, Issue 5 679-G685, Copyright © 1986 by American Physiological Society
Specific binding and degradation of somatostatin by membrane vesicles from pig gut
M. Weber, T. Cole and J. M. Conlon
Plasma membrane vesicles were prepared from the basolateral face of pig
small intestinal epithelial cells and were enriched in the activity of
Na+-K+-ATPase (9-fold relative to the cell homogenate) and ranged in size
from 0.15 to 0.40 micron diam. Incubation of somatostatin-14 and
[125I-Tyr11]-somatostatin-14 with the vesicles at 37 degrees C resulted in
rapid proteolytic degradation of the peptides. Metabolites were isolated by
reverse-phase high-performance liquid chromatography and identified by
amino acid composition. Cleavages between Ala1-Gly2, Phe6-Phe7, Phe7-Trp8,
and Thr10-Phe11 were observed, indicative of aminopeptidase and
endopeptidase action. Degradation was inhibited by 1,10-phenanthroline and
by bacitracin, and in the presence of these inhibitors and at 21 degrees C
binding of [125I-Tyr11]somatostatin-14 to the vesicles was observed.
Binding was inhibited in a concentration-dependent manner by
somatostatin-14 (half-maximal inhibition at 2.0 +/- 0.1 nM) and by
somatostatin-28 (0.8 +/- 0.1 nM) but not by structurally unrelated
peptides. The rate of degradation of [125I-Leu8, D-Trp22,
Tyr25]somatostatin-28 by basolateral membrane was less than 20 fold that of
[125I-Tyr11]somatostatin-14 and a two- to three-fold enhanced binding to
the vesicles was observed. Analysis of the inhibition of binding of this
analogue by somatostatin-28 indicates the presence of single class of
binding site with Kd = 1.3 +/- 0.3 nM. Rapid degradation but no specific
binding of somatostatin-14 by brush-border membranes was observed.(ABSTRACT
TRUNCATED AT 250 WORDS)
