The turnover of glycerol and acyl moieties of cardiolipin.

The dynamical behavior of mitochondria has attracted much attention, but little is known about the dynamics of mitochondrial lipids, specifically cardiolipin (CL). Here, we estimated the turnover of select molecular species of CL in mammalian cell cultures and compared it to the turnover of other lipids, including phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylinositol. Cells were labeled with myristic acid, 9,10-²H₂-oleic acid, or D-[U-¹³C₆]-glucose and analyzed by mass spectrometry at different time points of pulse-chase experiments. The turnover of glycerol groups was monitored by specific isotopologues that carried ¹³C primarily in the glycerol carbons, whereas the turnover of acyl groups was monitored by molecular species that carried myristoyl or ²H₂-oleoyl groups. We found that the turnover of CL, but not of mitochondrial PC and PE, was substantially slower than the turnover of other cellular phospholipids. In dioleoyl-PC and dioleoyl-PE, the acyl turnover was faster than the glycerol turnover, indicating continuous deacylation and reacylation of the oleoyl residues. In contrast, the acyl turnover was similar to the glycerol turnover in tetraoleoyl-CL, suggesting that oleoyl remodeling did not take place continuously in endogenous CL. We conclude that CL, once assembled in mitochondrial membranes, remains largely inert to degradation and acyl remodeling.