:Phosphatidylinositol 3-phosphate

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| ImageFile = Phosphatidylinositol-3-phosphate.svg

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| OtherNames = sn-1-stearoyl-2-arachidonoyl phosphatidylinositol 3-phosphate

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| Abbreviations = PtdIns3P
PtdIns(3)P
PI3P
PI(3)P

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| PubChem = 6857403

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|Section2={{Chembox Properties

| Formula = C₁₁H₂₀O₁₆P₂

| MolarMass = 470.214 g/mol, neutral with fatty acid composition - 18:0, 20:4

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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.{{cite journal | vauthors = Gillooly DJ, Simonsen A, Stenmark H | title = Cellular functions of phosphatidylinositol 3-phosphate and FYVE domain proteins | journal = The Biochemical Journal | volume = 355 | issue = Pt 2 | pages = 249–58 | date = April 2001 | pmid = 11284710 | pmc = 1221734 | doi = 10.1042/0264-6021:3550249 }}

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.{{cite journal | vauthors = De Craene JO, Bertazzi DL, Bär S, Friant S | title = Phosphoinositides, Major Actors in Membrane Trafficking and Lipid Signaling Pathways | journal = International Journal of Molecular Sciences | volume = 18 | issue = 3 | pages = 634 | date = March 2017 | pmid = 28294977 | pmc = 5372647 | doi = 10.3390/ijms18030634 | doi-access = free }}

Both FYVE domains and PX domains – found in proteins such as SNX1, HGS, and EEA1 – bind to PtdIns3P.{{cite journal | vauthors = Stenmark H, Aasland R, Driscoll PC | title = The phosphatidylinositol 3-phosphate-binding FYVE finger | journal = FEBS Letters | volume = 513 | issue = 1 | pages = 77–84 | date = February 2002 | pmid = 11911884 | doi = 10.1016/s0014-5793(01)03308-7 | doi-access = | bibcode = 2002FEBSL.513...77S }}

The majority of PtdIns3P appears to be constitutively synthesised by the class III PI 3-kinase, PIK3C3 (Vps34), at endocytic membranes. Class II PI 3-kinases also appear to synthesise PtdIns3P, their activity however appears to be regulated by a range of stimuli, including growth factors. This suggests that specific pools of PtdIns3P may be synthesised upon cell stimulation.