The acylation of 1-acyl sn-glycero-3-phosphorylcholine by glial and neuronal nuclei and derived neuronal unclear envelopes: a comparison of unclear and microsomal membranes

Abstract

A neuronal nuclear fraction (N1), a glial nuclear fraction (N2) and a fraction containing microsomal membranes (P3) were isolated from homogenates of cerebral cortices of 15 day old rabbits. A nuclear envelope fraction (E) was prepared from fraction N1. In comparison with the parent fraction N1, fraction E had a much lower yield of protein (0.077 mg/g cerebral cortex), a low specific DNA content, an 8-fold higher specific phospholipid content (0.85 .mu.mol phospholipid phosphate/mg protein) and a very similar phospholipid distribution profile. Using 100, 50 and 25 .mu.M 1-acyl-sn-glycero-3-phosphorylcholine (labeled with [3H]palmitate) and 100 .mu.M oleoyl CoA, the activity of acyl-CoA:1-acyl-sn-glycero-3-phosphorylcholine acyltransferase was studied in vitro. Fractions N1 and N2 had specific activities which were 2-3 times the specific activities shown for fraction P3. Fraction E was particularly enriched in this acylation activity and had specific activities which were 6 times those of fraction N1 and 11-19 times those of fraction P3. The existence of nuclear acyl-CoA:1-acyl-sn-glycero-3-phosphorylcholine acyltransferase activity was indicated as was a particularly high concentration of this enzyme within the nuclear envelope. In assays of lysolecithin-lysolecithin transacylase activity, fraction N2 (glial nuclei) showed the highest specific activities, being 3-4 times those of fractions N1 or P3. This transacylase activity (N2) was as high as 40% of the corresponding acyltransferase activity measured in this fraction using oleoyl CoA as acyl donor.