Phosphatidylinositol 3-phosphate (PI3P) is a phospholipid found in cell membranes that helps to recruit a range of proteins, many of which are involved in protein trafficking, to the membranes.

It is the product of both the class II and III phosphoinositide 3-kinases (PI 3-kinases) activity on phosphatidylinositol.

[1] PtdIns3P is dephosphorylated by the myotubularin family of phosphatases, on the D3 position of the inositol ring, and can be converted to PtdIns(3,5)P2 by the lipid kinase PIKfyve.

[3] The majority of PtdIns3P appears to be constitutively synthesised by the class III PI 3-kinase, PIK3C3 (Vps34), at endocytic membranes.

This suggests that specific pools of PtdIns3P may be synthesised upon cell stimulation.