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  2. Factors to consider in using [U-C]palmitate for analysis of sphingolipid biosynthesis by tandem mass spectrometry

Factors to consider in using [U-C]palmitate for analysis of sphingolipid biosynthesis by tandem mass spectrometry

  • J Lipid Res. 2011 Aug;52(8):1583-94. doi: 10.1194/jlr.D015586.
Christopher A Haynes 1 Jeremy C Allegood Elaine W Wang Samuel L Kelly M Cameron Sullards Alfred H Merrill Jr
Affiliations

Affiliation

  • 1 Newborn Screening and Molecular Biology Branch, Centers for Disease Control and Prevention, Atlanta, GA, USA.
Abstract

This study describes the use of a stable-isotope labeled precursor ([U-¹³C]palmitate) to analyze de novo sphingolipid biosynthesis by tandem mass spectrometry. It also describes factors to consider in interpreting the data, including the isotope's location (¹³C appears in three isotopomers and isotopologues: [M + 16] for the sphingoid base or N-acyl fatty acid, and [M + 32] for both); the isotopic enrichment of palmitoyl-CoA; and its elongation, desaturation, and incorporation into N-acyl-sphingolipids. For HEK293 cells incubated with 0.1 mM [U-¹³C]palmitic acid, ∼60% of the total palmitoyl-CoA was ¹³C-labeled by 3 h (which was near isotopic equilibrium); with this correction, the rates of de novo biosynthesis of C16:0-ceramide, C16:0-monohexosylceramide, and C16:0-sphingomyelins were 62 ± 3, 13 ± 2, and 60 ± 11 pmol/h per mg protein, respectively, which are consistent with an estimated rate of appearance of C16:0-ceramide using exponential growth modeling (119 ± 11 pmol/h per mg protein). Including estimates for the very long-chain fatty acyl-CoAs, the overall rate of sphingolipid biosynthesis can be estimated to be at least ∼1.6-fold higher. Thus, consideration of these factors gives a more accurate picture of de novo sphingolipid biosynthesis than has been possible to-date, while acknowledging that there are inherent limitations to such approximations.

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