Modulation of lyso-platelet activating factor: acetyl-CoA acetyltransferase from rat splenic microsomes. The role of cyclic AMP-dependent protein kinase.

Incubation of rat splenic microsomes with the catalytic subunit of cyclic AMP-dependent protein kinase in the presence of Mg-ATP stimulated 2-3-fold lyso-platelet-activating factor: acetyltransferase activity. This activation was due to an increase in the Vmax of the acetylation reaction, whereas the Km for acetyl-CoA was not affected. The ATP derivative, AMPPNP, could not replace ATP and preincubation of the microsomes with the heat-stable inhibitor of protein kinase prevented the activation by Mg-ATP obtained in the presence of the protein kinase. Activation of the acetylation reaction by the protein kinase was reversible. Evidence is provided that the reversal of activation is due to dephosphorylation of the enzyme. These data provide evidence that in vitro lyso-platelet-activating factor: acetyltransferase from splenic microsomes is regulated by phosphorylation.