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Journal of Lipid Research, Vol 34, 1783-1792, Copyright © 1993 by Lipid Research, Inc.
Purification of the major substrate for palmitoylation in rat adipocytes: N-terminal homology with CD36 and evidence for cell surface acylation
A Jochen and J Hays
Department of Medicine, Medical College of Wisconsin, Zablocki Veterans Administration Hospital, Milwaukee 53295.
We previously reported that incubating rat adipocytes with [3H]palmitate
predominantly labeled an 85-kDa protein. The labeling was more intensive in
the presence of insulin and had characteristics consistent with covalent
fatty acylation (Jochen et al. 1991. Biochem. Biophys. Res. Commun. 177:
797-801). In order to determine the significance of this finding we
purified the 85-kDa protein, determined its N-terminal sequence, and
further characterized its interactions with long-chain fatty acids. The
[3H]palmitate-labeled 85-kDa protein was purified from rat adipocyte
membranes using the following sequence of procedures: i) affinity
chromatography with wheat germ agglutinin- agarose, ii) ion exchange
chromatography with DEAE-Sepharose, and iii) SDS-polyacrylamide gel
electrophoresis. The resulting labeled protein was sequenced through 30
amino acid residues. With the exception of one conserved substitution, the
sequence was identical to CD36 (platelet membrane glycoprotein IV). Further
characterization of the 85-kDa protein revealed it was heavily
N-glycosylated and possessed a cell surface domain. Labeling of the 85-kDa
protein with palmitate was compared in control cells, insulin-treated
cells, and cells whose energy was depleted with 2,4-dinitrophenol. Insulin
and energy depletion increased labeling approximately 3-fold and 12-fold,
respectively. Labeling performed in the presence of energy depletion
possessed all of the characteristics of covalent protein acylation. In
addition, there was a close association between the ability of energy
depletion to increase labeling of the 85-kDa protein and its ability to
inhibit depletion of [3H]palmitate from the extracellular incubation media.
These results suggest that the major substrate for fatty acylation in
adipocytes is a cell surface membrane protein related to CD36 and that this
acylation has the unusual properties of being independent of intracellular
metabolic energy and of occurring on an exofacial epitope of the protein.

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Copyright © 1993 by the American Society for Biochemistry and Molecular Biology.
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