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Antibodies & Assays to Phosphatidylserine & Annexin V

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Apoptosis pathway using Annexin V.
Phosphatidylserine (PS) is normally confined in the inner membrane leaflet of viable cells. The translocation of PS to the exposed membrane surface is an early event in apoptosis, where it serves as a signal for the attack of phagocytic cells. Translocation of PS is not due to a generalized change in the membrane but is controlled by the activity of a PS translocase enzyme. Another early membrane event that is characteristic of apoptosis is the eruption of cell surface blebs. It is mainly at the surface blebs that the PS is exposed.

Annexins are a family of structurally related proteins that can bind specifically to cellular membranes. Annexin V, in particular, has a very high affinity for membranes containing the negatively charged phospholipid phosphatidylserine (PS). Specific binding is rapid and calcium-dependent.

Merck provides a suite of antibodies, inhibitors, proteins and assays to help detect phosphatidylserine (PS) in apoptotic cells.


Product Highlight:
ApopNexin™ Annexin V FITC Apoptosis Kit
ApopNexin™ Annexin V FITC Apoptosis Kit
Human peripheral blood lymphocytes induced with an anti-Fas antibody for 3–4 hours and then assayed with ApopNexin FITC and propidium iodide. Results obtained by fluorescence microscopy show that apoptotic cells have ApopNexin FITC bound to the PS on the outer membrane surface (Panel A). As apoptosis progressed, the plasma membrane becomes permeable, and the propidium iodide is able to enter into the cell and bind to cellular DNA (Panels B and C). Necrotic cells are detected by intense propidium iodide staining of the cytoplasm, due to complete disruption of the plasma membrane (Panel D). 
The ApopNexin™ FITC Apoptosis Detection Kit is designed to detect the appearance of Phosphatidylserine (PS) in the outer leaflet of the membrane of the cell. The system uses Annexin V conjugated to either FITC or Biotin to allow for convenient quantitative assays. The counterstain Propidium Iodide is included to differentiate the apoptotic and necrotic cells.

ApopNexin FITC binding can be analyzed by flow cytometry or fluorescence microscopy in less than one hour. It may be used in conjunction with other fluorescent cell surface markers. This versatile approach also allows bicolor fluorescence experiments for multiparameter cell surface analysis. Fixation can be performed after Annexin V binding for further analysis of other cellular antigens.


Product Highlight:
FlowCellect™ Annexin Red Kit
Merck’s FlowCellect Annexin Red Kit provides a rapid and convenient assay to monitor early and late apotosis. The kit includes recombinant Annexin V conjugated to a red sensitive dye, CF647, to provide maximum sensitivity and 7-AAD, a cell impermeant dye which is an indicator of cell membrane structural integrity along with an assay buffer. 7-AAD is excluded from live, healthy cells and early apoptotic cells but stains late stage apoptotic and dead cells with red fluorescence by binding to nucleic acids in the cell. After staining cells with Flowcellect Annexin Red Kit, three populations of cells can be identified in this assay:
  • Non-apoptotic cells: Annexin V(-) and 7-AAD(-)
  • Early apoptotic cells: Annexin V(+) and 7-AAD(-)
  • Late stage apoptotic or dead cells: Annexin V(+) and 7-AAD(+)
$’s FlowCellect Annexin Red Kit provides a rapid and convenient assay to monitor early and late apotosis.
Dot plots depicting Jurkat cells treated with multiple concentration of inducers and stained using FlowCellect™ Annexin Red Kit. Jurkat cells were untreated (Plot A), or treated with 0.1 uM (Plot B) or with 3 uM Staurosporine (Plot C).

Product Highlight:
Anti-Phosphatidylserine, clone 1H6
Anti-Phosphatidylserine may be used to detect translocation of the membrane phospholipid phosphatidylserine (PS).
Flow Cytometry: Jurkat cells were cultured without (A) and with (B) Fas ligand vesicles, then stained using anti-phosphatidylserine, clone 1H6 or a normal mouse IgG, followed by a goad F(ab’)2 anti-mouse IgG PE-conjugate. The antibody detects surface phosphatidylserine in apoptosis-induced cells. (Click image to enlarge.)
Anti-Phosphatidylserine may be used to detect translocation of the membrane phospholipid phosphatidylserine (PS) from the inner to the outer cell membrane leaflet; it provides a simple alternative to Annexin V for quantitation of apoptosis.


Merck's Family of Phosphatidylserine (PS) Detection Assays & Antibodies

DescriptionCatalog No.Assays
ApopNexin Annexin V FITC Apoptosis Kit APT750 100 assays
Annexin V-FITC Apoptosis Detection Kit PF032 100 tests
Annexin V-FITC Apoptosis Detection Kit II CBA059 20 tests
Annexin V-Biotin Apoptosis Detection Kit PF036 100 tests
Annexin V-PE Apoptosis Detection Kit CBA060 25 or 100 tests
FlowCellect Annexin Red Kit FCCH100108 100 tests
Anti-Phosphatidylserine, clone 1H6 05-719 200 µg