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I Olsson, M Lantz, AM Persson and K Arnljots
Department of Medicine, University of Lund, Sweden.
The processing and intracellular transport of lactoferrin of the neutrophil
specific granules was investigated by biosynthetic labeling with
(14C)leucine of bone marrow cells from healthy individuals and patients
with chronic myeloid leukemia. Lactoferrin was precipitated with
antilactoferrin serum and the immunoprecipitates were analyzed by sodium
dodecyl sulfate (SDS), polyacrylamide gel electrophoresis (PAGE) followed
by fluorography. In contrast to myeloperoxidase of azurophil granules,
lactoferrin was not synthesized as a larger precursor, and it was not found
to be phosphorylated. The transfer to granules of newly synthesized
lactoferrin was demonstrated in pulse-chase labeling experiments followed
by centrifugation of cell homogenate in a Percoll gradient. Monensin, which
exchanges protons for Na+ and NH4+ cation, blocked the transfer completely,
indicating a need for acidification mechanisms. Unlike myeloperoxidase,
newly synthesized lactoferrin rapidly became resistant to endoglycosidase
H, indicating a transport through the medial and transcisternae of the
Golgi apparatus with conversion of "high mannose" to "complex"
oligosaccharide side chains. Intracellular transfer of some major
neutrophil azurophil and specific granule constituents is obviously
regulated differently. Lactoferrin seems to be processed like proteins
destined for secretion, while myeloperoxidase is processed more or less
like lysosomal enzymes.
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| Copyright © 1988 by American Society of Hematology Online ISSN: 1528-0020 | |||||||||
