[Studies on acetyl-CoA:lyso platelet activating factor acetyltransferase of rat spleen microsomes--solubilization and...

Acetyl-CoA: lyso platelet activating factor (1-O-alkyl-2-lyso-sn-glycero-3-phosphorylcholine) acetyltransferase was solubilized from rat spleen microsomes with ultrasonic irradiation in the presence of 25% glycerol and partially purified by Sepharose 6B column chromatography. The overall yield of this procedures was approximately 26% and its specific activity was 1.7 times compared with that of original microsomes. The solubilized enzyme was extremely labile, but did not lose the activity for several weeks at -70 degrees C. The solubilized enzyme was remarkably susceptible to various kinds of metal ions. Furthermore, sulfhydryl reagents such as N-ethylmaleimide and p-chloromercuribenzoate profoundly inhibited the enzyme reaction, suggesting that the enzyme was -SH enzyme. The acetyltransferase activity was remarkably decreased by tryptic digestion of spleen microsomes, which indicated that the enzyme was located in the cytoplasmic surface of microsomal membranes. On the substrate specificity, the enzyme preferentially acetylated 1-O-hexadecyl-2-lyso-sn-glycero-3-phosphorylcholine and 1-O-octadecenyl-2-lyso-sn-glycero-3-phosphorylcholine as compared with other chain length at sn-1 position of lyso platelet activating factor, which may suggest that biologically potent molecular species of PAF are selectively synthesized. On the other hand, the enzyme also acetylated an acyl analog of lyso platelet activating factor. Some experimental results have shown that these two acetylation reaction presumably would be performed by the same enzyme.