Cardiolipin (bisphosphatidyl glycerol) is an important component of the inner mitochondrial membrane, where it constitutes about 20% of the total lipid. It is typically present in metabolically active cells of the heart and skeletal muscle, in the membranes of their mitochondria, mostly in the inner membrane, and consists roughly 20% of its lipids. It has also been observed in certain bacterial membranes. It serves as an insulator and stabilizes the activity of protein complexes important to the electron transport chain. It also "glues" them together. Cardiolipin is a "double" phospholipid because it has four fatty acid tails, instead of the usual two. [Wikipedia]