Question: Is diphosphatidylglycerol (cardiolipin) a phospholipid of the mitochondrial membranes?

Context:
A unique organelle for studying membrane biochemistry is the mitochondrion whose functionality depends on a coordinated supply of proteins and lipids. Mitochondria are capable of synthesizing several lipids autonomously such as phosphatidylglycerol, cardiolipin and in part phosphatidylethanolamine, phosphatidic acid and CDP-diacylglycerol.
A small decrease of diphosphatidylglycerol also occurred in the hepatoma mitochondria inner membrane. 
Diphosphatidylglycerol was confined to the mitochondrial fraction, where it represented about 7% of the total phosphoacylglycerols. 
Mitochondrial membranes were isolated from the myocardium of young (4-month-old) and aged (33-month-old) male Long-Evans rats and compared in terms of cholesterol content and phospholipid and fatty acid composition. In aged rats, as compared to young, the major observations include: markedly higher cholesterol content; increased percentage of sphingomyelin and diphosphatidylglycerol (cardiolipin); 
The polyglycerophosphatides (typified by diphosphatidylglycerol) were apparently synthesized in situ by intramitochondrial membrane-bound enzymes using CDP-diglycerides as intermediates. 
Both the mitochondrial and microsomal fractions contained significant proportions of solvent front phospholipid (SFP) and whereas the mitochondrial SFP displayed the relatively unsaturated fatty acid composition characteristic of diphosphatidylglycerol (cardiolipin), the fatty acids of the microsomal SFP were distinctly more saturated.
Ten to 15% of microsomal radioactive CDP-diglycerides was transferred to mitochondrial membranes and incorporated into mitochondrial radioactive lipids identified as phosphatidylglycerol, phosphatidylglycerophosphate, and, when [14C]linoleoyl CDP-diglycerides were used, diphosphatidylglycerol (cardiolipin).
The enzyme responsible for the conversion of phosphatidylglycerol to diphosphatidylglycerol (cardiolipin) in the presence of cytidine diphosphate diacylglycerol is firmly associated with mitochondrial membranes and is not extracted with hypotonic or hypertonic media or with nonionic detergents.
The mechanism of cardiolipin (diphosphatidylglycerol) biosynthesis was examined in mitochondria and outer and inner mitochondrial membranes prepared from guinea pig and rat livers to determine whether this formation from phosphatidylglycerol was absolutely dependent on cytidinediphosphodiglyceride, as previously reported for intact mitochondria.
In isolated mitochondrial outer membranes, cardiolipin (diphosphatidylglycerol) increased CPT1 activity 4-fold and the Km for carnitine 6-fold.
Ten to 15% of microsomal radioactive CDP-diglycerides was transferred to mitochondrial membranes and incorporated into mitochondrial radioactive lipids identified as phosphatidylglycerol, phosphatidylglycerophosphate, and, when [14C]linoleoyl CDP-diglycerides were used, diphosphatidylglycerol (cardiolipin).
90% or more of the phospholipid, cardiolipin was found in the mitochondrial membranes of wild type and petite yeast.
Furthermore, the same mechanism for the biosynthesis of cardiolipin was operational in the outer and inner mitochondrial membranes.
The mechanism of cardiolipin (diphosphatidylglycerol) biosynthesis was examined in mitochondria and outer and inner mitochondrial membranes prepared from guinea pig and rat livers to determine whether this formation from phosphatidylglycerol was absolutely dependent on cytidinediphosphodiglyceride, as previously reported for intact mitochondria
Cardiolipin (CL) is a key phospholipid in mitochondrial membranes, playing important roles in maintaining the functional integrity and dynamics of mitochondria in animals and yeasts
Cardiolipin, the specific phospholipid of mitochondria, is involved in the biogenesis, the dynamics, and the supramolecular organization of mitochondrial membranes
Cardiolipin (CL), the signature phospholipid of mitochondrial membranes, is crucial for both mitochondrial function and cellular processes outside of the mitochondria
Since it has been recognized that mitochondria are crucial not only for energy metabolism but also for other cellular functions, there has been a growing interest in cardiolipin, the specific phospholipid of mitochondrial membranes
Cardiolipin, the main anionic phospholipid in mitochondrial membranes, is expected to be a determinant in this adaptive mechanism since it modulates the activity of most membrane proteins
Ten to 15% of microsomal radioactive CDP-diglycerides was transferred to mitochondrial membranes and incorporated into mitochondrial radioactive lipids identified as phosphatidylglycerol, phosphatidylglycerophosphate, and, when [14C]linoleoyl CDP-diglycerides were used, diphosphatidylglycerol (cardiolipin)
Cardiolipin is normally localized to the inner mitochondrial membrane; however, when cardiolipin becomes externalized to the surface of dysregulated mitochondria, it promotes inflammasome activation and stimulates the elimination of damaged or nonfunctional mitochondria by mitophagy
In isolated mitochondrial outer membranes, cardiolipin (diphosphatidylglycerol) increased CPT1 activity 4-fold and the Km for carnitine 6-fold. 
Increasing levels of cardiolipin differentially influence packing of phospholipids found in the mitochondrial inner membrane.
Here, we used Saccharomyces cerevisiae subjected to conditions that affect mitochondrial metabolism as a model to determine the possible role of cardiolipin in stress adaptation. 
This decline of respiration was attributed to a progressive diminution of the number of mitochondria in copper-treated cells, based on the demonstration of the concomitant decline of (1) cardiolipin (diphosphatidylglycerol) and cytochrome aa3 (cytochrome oxidase), two specific markers of mitochondrial inner membrane, and (2) fumarase activity, a specific marker of mitochondrial matrix space.
Diphosphatidylglycerol (DPG) or cardiolipin, a specific component of the inner mitochondrial membrane, represents about 4% of the total lipid content.
Experimental results confirmed that the biosynthesis of cardiolipin, from the membrane-bound radioactive phosphatidylglycerol in intact mitochondria isolated from guinea pig and rat liver, was absolutely dependent on CDP-diglycerides and required the addition of divalent cations.
We have shown that decrease of cardiolipin in mitochondrial membrane occurs early during ischemia, and only during the irreversible phase of ischemia are phosphatidylethanolamine and phosphatidylcholine broken down.
Partial purification of diphosphatidylglycerol synthetase from liver mitochondrial membranes.
A small decrease of diphosphatidylglycerol also occurred in the hepatoma mitochondria inner membrane.

Answer: Yes, diphosphatidylglycerol (cardiolipin) is a phospholipid of the mitochondrial membranes.
Exact answer: yes