The Phosphatidylinositol Synthase-Catalyzed Formation of Phosphatidylinositol Does Not Exhibit Acyl Chain Specificity

Phosphatidylinositol (PI) and its phosphorylated forms are required for many critical cellular processes. PI is highly enriched at its sn-1 and sn-2 positions, the major species being 1-stearoyl-2-arachidonoyl PI (18:0/20:4 PI). This enrichment is achieved in part through enzymatic acyl chain specificity in PI synthesis. Here we characterize the acyl chain specificity of phosphatidylinositol synthase (PIS), which is involved in the terminal step of PI synthesis. Unlike several other enzymes involved in PI synthesis, PIS appears to exhibit no acyl chain specificity toward its substrates. Thus, enrichment of newly formed PI occurs prior to the terminal synthesis step.