The phospholipid composition of membranes can influence the physiological 
functioning of the cell or subcellular organelle. This association has been 
previously demonstrated in skeletal muscle, where cellular or subcellular 
membrane, specifically mitochondria, phospholipid composition is linked to 
muscle function. However, these observations are based on whole mixed skeletal 
muscle analysis, with little information on skeletal muscles of differing 
fiber-type compositions. These past approaches that used mixed muscle may have 
misidentified outcomes or masked differences. Thus, the purpose of this study 
was to compare the phospholipid fatty acid composition of subsarcolemmal (SS) 
mitochondria isolated from slow-twitch postural (soleus), fast-twitch highly 
oxidative glycolytic locomotory (red gastrocnemius), and fast-twitch oxidative 
glycolytic locomotory (plantaris) skeletal muscles. The main findings of the 
study demonstrated unique differences between SS mitochondrial membranes from 
postural soleus compared to the other locomotory skeletal muscles examined, 
specifically lower percentage mole fraction of phosphatidylcholine (PC) and 
significantly higher percentage mole fraction of saturated fatty acids (SFA) and 
lower n6 polyunsaturated fatty acids (PUFA), resulting in a lower unsaturation 
index. We also found that although there was no difference in the percentage 
mole fraction of cardiolipin (CL) between skeletal muscle types examined, CL of 
soleus mitochondrial membranes were approximately twofold more SFA and 
approximately two-thirds less PUFA, resulting in a 20-30% lower unsaturation and 
peroxidation indices. Thus, the results of this study indicate unique membrane 
lipid composition of mitochondria isolated from different skeletal muscle types, 
a potential consequence of their respective duty cycles.