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J. Biol. Chem., Vol. 283, Issue 6, 3676-3687, February 8, 2008

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Electrospray Ionization Mass Spectrometry and Exogenous Heavy Isotope-labeled Lipid Species Provide Detailed Information on Aminophospholipid Acyl Chain Remodeling^*

From the Institute of Biomedicine, Department of Biochemistry, University of Helsinki, Helsinki 00014, Finland

Mammalian cells maintain the phospholipid compositions of their different membranes remarkably constant. Beside de novo synthesis, degradation, and intracellular trafficking, acyl chain remodeling plays an important role in phospholipid homeostasis. However, many key details of this process remain unresolved, largely because of limitations of existing methodologies. Here we describe a novel approach that allows one to study metabolism of individual phospholipid species in unprecedented detail. Forty different phosphatidylethanolamine (PE) or -serine (PS) species with a deuterium-labeled head group were synthesized and introduced to BHK21 or HeLa cells using cyclodextrin-mediated transfer. Their metabolism was then monitored in detail by electrospray ionization mass spectrometry. Atypical PE and PS species were rapidly remodeled at both sn1 and sn2 position, yielding a molecular species profile similar to that the endogenous PE and PS. In contrast, remodeling of exogenous species identical or similar to major endogenous ones was more limited and much slower. Major differences in remodeling pathways and kinetics were observed between species within a class, as well as between corresponding PE and PS species. These data along with those obtained with pharmacological inhibitors strongly suggest that multiple lipid class-specific A-type phospholipases and acyl transferases are involved in aminophospholipid remodeling. In conclusion, the approach described here provides highly detailed information on remodeling of exogenously added (amino)glycerophospholipids and should thus be very helpful when elucidating the proteins and processes maintaining molecular species homeostasis.

Received for publication, November 8, 2007 , and in revised form, December 4, 2007.

^* This project was supported in part by the Finnish Academy, Sigrid Jusélius Foundation, Emil Aaltonen Foundation, and University of Helsinki Funds. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. S1-S4 and supplemental Note S1.

¹ These authors contributed equally to this work.

² To whom correspondence should be addressed: Institute of Biomedicine, Dept. of Biochemistry, PL 63, 00014 University of Helsinki, Finland. Tel.: 358-9-19125413; Fax: 358-9-19125444; E-mail: martin.hermansson{at}helsinki.fi.

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