Transfer of PC and PCOOH from liposomes to mitochondria in the absence vs. presence of StarD4 or SCP-2. Reaction mixtures containing liver mitochondria (0.6 mM total lipid) and DMPC/POPC (1:1 mol/mol) SUVs (0.06 mM total lipid) spiked with a trace of either [14C]POPC or [14C]POPC-OOH in pH 7.5 MS buffer at 37 °C were incubated in the absence or presence of 1 µM StarD4 or SCP-2. At the indicated times, samples were removed, centrifuged, and radioactivity in the mitochondrial fraction was measured. First-order kinetic plots for analyte acquisition by mitochondria are shown, the data points representing the following: POPC (○), POPC/StarD4 (●), POPC-OOH (△), POPC-OOH/StarD4 (▲), POPC/SCP-2 (▼), POPC-OOH/SCP-2 (■). Plotted values are means ± SD (n = 3).