Figure 1: SILEC-SF uses whole cell internal standards to quantify acyl-CoAs in subcellular compartments.

A) ¹⁵N₁¹³C₃-isotope labeled vitamin B5 (VB5) is incorporated into the coenzyme A (CoA) moiety such that acyl-CoAs across all acyl (R group) species are isotope labeled. This can be detected after fragmentation (MS2), which results in neutral loss of an unlabeled fragment (NL 507). B) SILEC-SF workflow: internal standards were generated through isotope labeling, internal standards were added to samples as whole cells prior to cell lysis and separation of subcellular compartments by fractionation. The analyte and internal standard in each fraction were analyzed simultaneously by LC-MS and relative quantities are determined between samples.