JBC, Vol. 250, Issue 17, 6779-6785, Sep, 1975
Isolation and characterization of cytidine diphosphate diglyceride from beef liver
W. Thompson and G. MacDonald
Cytidine diphosphate diglyceride was isolated from beef liver by a
combination of silicic acid column, DEAE-cellulose column, and this layer
chromatography. The product (5.8 to 17.4 mumol/kg of liver) contained
cytidine/phosphate/fatty acids in the molar proportions 1.05/2.0/2.05
(theoretical, 1.0/2.0/2.0) (average for three preparations). The
liponucleotide was split quantitatively by a partially purified hydrolase
from Escherichia coli, specific for CDP-diglyceride, (Raetz, C. R. H.,
Hirschberg, C. B., Dowhan, W., Wickner, W. T., and Kennedy, E. P. (1972) J.
Biol. Chem. 247, 2245-2247) into phosphatidic acid and a water-soluble
nucleotide that was chromatographically identical with CMP. No dCMP was
located in these hydrolysates. The liver liponucleotide was more effective
than a synthetic preparation of CDP-diglyceride in promoting the formation
of phosphatidylinositol with guinea pig brain microsomes. The fatty acid
composition of CDP-diglyceride was compared with metabolically related
phospholipids from beef liver. The liponucleotide had a similar composition
to phosphatidylinositol, characterized by a high level of stearate and with
arachidonate as the major unsaturated fatty acid. The content of
arachidonate in both lipids was significantly higher than that in
phosphatidic acid. The profile of fatty acids of cardiolipin was quite
unlike that of CDP-diglyceride. These findings suggest several alternatives
for the metabolic origins of beef liver CDP-diglyceride: (a)
CDP-diglyceride is formed from an atypical pool of phosphatidic acid, (b)
the enzyme is selective for arachidonoyl-containing species of phosphatidic
acid, (c) the liponucleotide may also be derived from phosphatidylinositol
by the back-reaction of CDP-diglyceride: inositol phosphatidyltransferase.