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. 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. Furthermore, the 
same mechanism for the biosynthesis of cardiolipin was operational in the outer 
and inner mitochondrial membranes. This biosynthesis was associated with both 
the outer and inner mitochondrial membranes prepared from guinea pig liver, but 
only with the inner mitochondrial membranes prepared from rat liver. The release 
of radioactive glycerol was also measured, but the amount obtained did not 
satisfy the stoichiometric requirement for CDP-diglyceride-independent 
biosynthesis of cardiolipin from 2 mol of phosphatidylglycerol with the 
liberation of 1 mol of glycerol. Therefore, it was concluded that this mechanism 
is not involved in the biosynthesis of cardiolipin in mitochondrial and 
submitochondrial membranes prepared from guinea pig and rat liver.