FIGURE 2.
A, in vitro SPT activity with various acyl-CoA substrates in control, SPTLC1-, SPTLC2-, and SPTLC3-overexpressing HEK293 cells. SPTLC3-overexpressing cells showed a significantly higher activity with lauroyl (C12)- and myristoyl (C14)-CoA compared with cells expressing the empty vector or the subunits SPTLC1 or SPTLC2. The activity with stearoyl and oleoyl-CoA was comparable for all cell lines (for comparison the activity with palmitoyl-CoA is defined as 100%). B, effect of serine supplementation on C16-SA generation in cultured HEKCnt and HEKSPTLC3 cells. Cells were treated with FB1 (24 h), and the accumulated C16-SA was quantified by LC-MS. A significant buildup of C16-SA was seen in SPTLC3-expressing cells but not in control cells. The addition of l-serine (10 mm) to the cell culture medium of SPTLC3 cells increased the generation of C16-SA ∼4-fold.