Annexin V - Biotin

Apoptosis, the physiological process of cell death, is a naturally occurring phenomenon.

It is normally a tightly regulated process; however, if deregulated, tumor growth can result.

Apoptotic processes can be measured in the laboratory easily and most effectively by using Fluorescently-labeled Annexin V protein to stain cells and analyze them via flow cytometry.

With Biotin-labeled Annexin V, you would follow the primary labeling of the cells with a SAV-conjugated to a fluorescent molecule for visualization (i.e.

FITC, PE, or any other).

It is a useful method to screen and analyze cells in a high throughput manner, resulting in a clearer understanding of the cellular response to various stimuli.

When cells are undergoing cell death, phosphatidylserine (PS), a phospholipid which makes up a portion of the cell membrane, will translocate to the outside-facing side of the membrane.

This translocation in the cell death mechanism exposes PS to the extracellular environment.

Annexin V, a 35-36 kDa phospholipid-binding protein, has a high affinity for PS (KDa=7nmol/l).

Once Annexin V is bound to the apoptotic cell it acts as a beacon for cells that have undergone apoptosis.

Annexin V is often conjugated to various fluorophores so the amount of signal can be measured and analyzed from labeled cells using a flow cytometer.

The translocation of PS to the outside or exposed side of the membrane is an early event in the apoptotic process.

Therefore, Annexin V staining is considered a marker for early stage apoptosis.

Often times, Annexin V is paired with Propidium Iodide (PI) stain in order to analyze for late-apoptotic or dead cells.

Early stage apoptotic cells will only take up the Annexin V stain but will remain PI negative, and late-stage apoptotic cells will be positive for both Annexin V and PI.