Fig. 3.

Rapid synthesis and slow turnover of propargylcholine-labeled phospholipids. (A) Time course of propargyl-Cho uptake and incorporation into phospholipids. NIH 3T3 cells were labeled with 1 mM propargyl-Cho in complete media for varying amounts of time and then stained with Alexa568-azide. The propargyl-Cho stain was photographed with a long exposure time (2 s, i–iii) or a short exposure time (30 ms, iv–ix). Note that propargyl-Cho incorporation is visible 30 min after addition to cells (ii) and continues to increase with time (ii–viii), saturating after about 24 h (ix). (B) Stability of propargyl-Cho-labeled phospholipids in cells. NIH 3T3 cells were labeled with 1 mM propargyl-Cho for 6 h and then chased with normal media for different amounts of time (i–iii). The intensity of the Alexa568-azide stain does not appreciably decrease after 24 h in culture, indicating the low turnover of propargyl-Cho phospholipids.