Loss of Phosphatidylinositol and Gain in Phosphatidate in Neutrophils Stimulated with Fmet-Leu-Phe

Summary

Neutrophils stimulated with fMetLeuPhe show a loss of phosphatidylinositol (PI) and a gain in phosphatidate (PA). In cells prelabeled with ³²P_i, it would be expected that the newly synthesized PA would have the same specific radioactivity as cellular ATP provided that PI loss is catalyzed by phospholipase C and the resultant diacylglycerol is phosphorylated by ATP. Instead, the specific radioactivity of the newly-formed PA was found to be less than a tenth of the specific radioactivity of ATP. The source of the newly formed PA is most likely to be PI because: (1) Increase in PA mass is accompanied by an equivalent decrease in mass of PI. (2) In cells pulse-labeled with [³H]glycerol, label lost from PI is recovered in PA. (3) Specific radioactivity of the new [³²P]PA is similar to the specific radioactivity of [³²P]PI. The most plausible explanation for these results is that PI is directly converted to PA by phospholipase D action. This conclusion is supported by observations that neither inositol phosphates nor diacylglycerol increase at the expense of PI or polyphosphoinositides in fMetLeuPhestimulated cells.