Transient activation of the acetyltransferase necessary for paf-acether biosynthesis in thrombin-activated platelets

Thrombin-activated platelets formed paf-acether (1-0-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine), a molecule susceptible to play a role in haemostasis and thrombosis, and its deacetylated analogue, lyso paf-acether, a biologically inactive molecule. We presently show the presence in human and rabbit platelet lysates of an acetyltransferase which transfers the acetyl moiety of acetyl-coenzyme A (acetyl-CoA) onto synthetic lyso paf-acether, yielding the fully active paf-acether molecule. Under our optimal standard conditions, 0.36 +/- 0.23 nmol paf-acether/10 min/mg proteins was formed by the acetyltransferase from resting human platelets. Upon thrombin stimulation, the acetyltransferase activity doubled within 30 s, reaching a maximum at 2 min (1.17 +/- 0.31 nmol paf-acether/10 min/mg proteins) and decreased progressively. Similar results were obtained using rabbit platelets. In addition we demonstrated that the activation and deactivation of the acetyltransferase correlated with the kinetics of paf-acether formation by thrombin-activated rabbit platelets. It is hypothesized that this enzyme may represent one of the regulating mechanism of paf-acether formation by platelets.