ALKYLGLYCEROPHOSPHATE ACETYLTRANSFERASE AND LYSO-PLATELET-ACTIVATING-FACTOR ACETYLTRANSFERASE, 2 KEY ENZYMES IN THE SYNTHESIS OF PLATELET-ACTIVATING-FACTOR, ARE FOUND IN NEURONAL NUCLEI ISOLATED FROM CEREBRAL-CORTEX

Neuronal nuclear fractions (N-1) isolated from cerebral cortices of 15 -day-old rabbits were enriched in two acetyltransferases involved in b iosynthetic pathways leading to platelet activating factor (PAF). Alky lglycerophosphate (AGP) acetyltransferase of the de novo biosynthetic path had specific activities in fraction N-1 which were 3-times those of the microsomal fraction (P3D) from cerebral cortex. Lyse PAF acetyl transferase of the remodelling path had specific activities in N-1 whi ch were 16-times those of P3D and 51-times those of the homogenate. Th e maximum specific activity observed for the N-1 AGP acetyltransferase was 1.4-times the corresponding N-1 lyso PAF acetyltransferase value. The pH optimum for the N-1 AGP acetyltransferase was within the alkal ine range (pH 8-9), while the N-1 lyso PAF acetyltransferase showed a much broader pH optimal range which extended over the neutral and phys iological pH values. Both acetyltranferases were inhibited by MgATP (0 .125-1 mM) or oleoyl CoA (2-10 mu M) However, the N-1 AGP acetyltransf erase could be distinguished from the N-1 lyso PAF acetyltransferase b y a greater sensitivity to MgATP inhibition. When NaF was not present in the assays, less of the product of N-1 AGP acetyltransferase was re covered, likely indicating a hydrolysis of the acetylated AGP, When th e AGP and lyso PAF substrates were combined in acetyltransferase assay s, the two N-1 acetylations appeared to proceed independently. The enr ichment of the acetyltransferases, and particularly the lyso PAF acety ltransferase, within the neuronal nuclear fraction is of particular in terest with respect to the intracellular effects of PAF which are cons idered to be involved in nuclear signalling mechanisms.