why most Annexin 5 products are conjugated? - Can't we use it on its own? (Oct/08/2010 )

I want to buy an Annexin 5 from Sigma but most products and kits got conjugated Annexin (e.g -FITC). I thought Annexin stains cells on its own like how Propidium Iodide does. I need to use it for flow cyto and don't know which one to buy.

Annexin 5 is the surface epitope that is recognized by the anti-Annexin 5 antibody you want to buy. That antibody should be conjugated, if you want to use it for FACS. I'd recommend APC conjugation, if you want to use PI as well... However, FITC should be working as well.

rsm

um...Annexin 5-FITC is not antibody, is it?

No, Annexin 5 is the surface epitope that is recognized by the anti-Annexin 5 antibody, which is conjugated to FITC.
http://www.biocompare.com/ProductListings/3194/Annexin-V-Antibodies.html?types=6-18937&sb=true

rsm

I'm talking about fluorescent dye labeled annexin v:

http://www.sigmaaldrich.com/catalog/ProductDetail.do?N4=A9210|SIGMA&N5=SEARCH_CONCAT_PNO|BRAND_KEY&F=SPEC

Oh, you're right, I didn't know that there was this distinction. However, you still need a method of detection of Annexin 5 binding. How do you want to do it, if not by fluorescent labelling?

most probably Annexin 5 is useless on its own so that's why they label it.

...i thought that annexin-5 recognizes phosphatidylserin which swiches onto the outer leaflet of the cell-membrane during apoptosis process!

annexin 5 is a phospholipid-binding protein (NO antibody) therefore it has to be labelled!!