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(Received for publication, January 10, 1997, and in revised form, May 28, 1997)
From the This study utilized fluorescent analogs to
characterize the intracellular transport and metabolism of
dihydroceramide (DH-Cer), an intermediate in de novo
sphingolipid biosynthesis. When
6-[N-(7-nitro-2,1,3-benzoxadiazol-4-yl)amino]hexanoyl-DH-Cer (C6-NBD-DH-Cer) was incubated with HT29, NRK, BHK, or HL-60
cells, it was efficiently converted to dihydrosphingomyelin and
dihydroglucosylceramide, and a number of other sphingolipids, with the
nature of the products depending on the cell line. In addition, complex
sphingolipids were formed that contained a desaturated (sphingosine)
backbone, indicating that DH-Cer (and/or its metabolites) were
substrates for the desaturase(s) that introduce the
4,5-trans double bond. Based on the kinetics and inhibitor
studies, double bond addition did not appear to occur with the complex
sphingolipids directly, but rather, during turnover and resynthesis.
The conversion of C6-NBD-DH-Cer to more complex
sphingolipids was highly stereoselective for the natural
D,erythro isomer of C6-NBD-DH-Cer.
Interestingly, the stereochemistry of the sphingoid base backbone also
affected the localization of fluorescent sphingolipids: the
D,erythro species appeared in the Golgi
apparatus, whereas other stereo-isomers accumulated in the endoplasmic
reticulum. In addition to C6-NBD-Cer and
C6-NBD-DH-Cer,
C6-NBD-4-D-hydroxy-DH-Cer gave rise to
formation of complex sphingolipids and localized at the Golgi
apparatus. These studies indicate that dihydroceramide is used as the
initial backbone of complex (glyco)sphingolipids, perhaps to avoid
build up of ceramide as an intermediate since this is such a potent bioactive compound. The stereoselectivity in transport and metabolism suggests that trafficking of ceramide is protein-directed rather than
simply a consequence of vesicular membrane flow.
Volume 272, Number 34,
Issue of August 22, 1997
pp. 21128-21136
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.
STRUCTURE-SPECIFIC METABOLISM AND INTRACELLULAR
LOCALIZATION
,
,
Department of Physiological Chemistry,
University of Groningen, A. Deusinglaan 1, 9713 AV Groningen, The
Netherlands and the ¶ Department of Biochemistry, Emory
University, Atlanta, Georgia 30322
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