The formation of phosphatidic acid de novo: a comparison of activities in neuronal nuclei and microsomes isolated from immature rabbit cerebral cortex.
The formation of phosphatidic acid from sn-glycerol 3-phosphate was studied in neuronal nuclear fraction N1 and a microsomal fraction P3, isolated from cerebral cortices of 15-day-old rabbits. Two assays were used, employing dithiothreitol, MgCl2, NaF and (A) sn-glycerol 3-phosphate, [14C]oleate, ATP and CoA or (B) sn-[3H]glycerol 3-phosphate and oleoyl-CoA. In both assays fraction N1 had specific rates of phosphatidic acid labelling (expressed per mumol phospholipid in the fraction) which were 5- to 6-times the corresponding values for P3. In contrast to N1, the formation of phosphatidic acid by fraction P3 was more sensitive to inhibition at high concentrations of oleoyl-CoA and was greatly dependent upon the presence of NaF. In the absence of this salt, P3 showed decreased phosphatidate formation and increased levels of radioactive monoacylglycerols. Using cerebral cortex, rough (R) and smooth (S) microsomal fractions were prepared, as was a microsomal fraction P from isolated nerve cell bodies. P had specific rates of phosphatidic acid labelling which were 2-3 times the values for P3, but were about 50% of the N1 values. This indicates a concentration of phosphatidate synthesis in the nucleus within the nerve cell. Specific rates for fraction R were higher and were similar to those of N1. In S, P3 and R the specific rates of phosphatidic acid synthesis paralleled specific RNA contents and indicated a location for phosphatidic acid synthesis within the rough endoplasmic reticulum.
Baker
R R
RR
Department of Medicine, University of Toronto, Canada.
Chang
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HY
D000818:Animals; D002467:Cell Nucleus / Q000032:analysis; D002540:Cerebral Cortex / Q000032:analysis*; D005994:Glycerophosphates / Q000378:metabolism; D008861:Microsomes / Q000032:analysis*; D009474:Neurons / Q000032:analysis*; D019301:Oleic Acid; D009829:Oleic Acids / Q000378:metabolism; D010712:Phosphatidic Acids / Q000032:analysis / Q000096:biosynthesis*; D012313:RNA / Q000032:analysis; D011817:Rabbits; D013347:Subcellular Fractions / Q000032:analysis
D005994:Glycerophosphates; D009829:Oleic Acids; D010712:Phosphatidic Acids; D019301:Oleic Acid; D012313:RNA; C029620:alpha-glycerophosphoric acid