Biochemical properties of the eosinophil cationic protein and demonstration
of its biosynthesis in vitro in marrow cells from patients with an
eosinophilia
I Olsson, AM Persson and I Winqvist
The eosinophil cationic protein (ECP), which has been shown to be secreted
both in vitro and in vivo, is a cytotoxic unique constituent of eosinophil
granules. To increase the understanding of the mechanisms behind the role
of the eosinophil as a cytotoxic effector in disease, a detailed
biochemical characterization of ECP was performed. A considerable molecular
heterogeneity was revealed when purified ECP was eluted isocratically from
a high-resolution cation exchange resin; the separation, reproducibly
achieved, of five components was probably due to hydrophobic interaction
with the resin. These polypeptides, which reacted quantitatively with
anti-ECP antiserum, showed molecular weights (mol wt) of 19,500 and 16,700
and showed almost identical amino acid compositions. The amino-terminal
sequence for one of the polypeptides was (in the standard one-letter code)
(R-P-X-Q-F-T-R-A-Q-W- F-A-I-Q-H-I-S-L-N-P-R-R-C-T-I-A-M-R-A-I-N-N-Y-). The
biosynthesis of ECP was demonstrated in marrow cells from patients with
eosinophilia using labeling with (14C)-leucine, followed by
immunoprecipitation with anti-ECP, sodium dodecyl sulfate-polyacrylamide
gel electrophoresis, and fluorography for visualization of labeled ECP.
Biosynthesis was demonstrated of mol wt 22,000 ECP, which may represent
precursor ECP, since with time some of it was processed into ECP with a mol
wt of 18,000 to 19,000. Monensin, a proton ionophore, blocked the
processing of mol wt 22,000 ECP. This study shows that ECP consists of a
family of similar polypeptides. These may, however, have different
biological activities.
Volume 67,
Issue 2,
pp. 498-503,
02/01/1986
Copyright © 1986 by The American Society of Hematology
