Detection of VAC-beta (annexin-8) in human placenta

A 36 kDa calcium/phospholipid binding protein in human placenta was identified as VAC-beta (annexin-8) by a combination of immunological and peptide mapping analyses. The protein is a minor product in placenta, accounting for less than 1% of extracted annexins. From 150 g of tissue, only 100 micrograms of the protein was isolated. By anion-exchange chromatography on diethylaminoethyl-cellulose annexin-8 coeluted with annexin-3. By gel filtration, the protein chromatographed as a broad peak, where half the product eluted as a monomer and half eluted as a heterodimer that was associated with a 10 kDa subunit. The combination of annexin-8 being a minor component in standard annexin preparations and it co-eluting with annexin-3 by ion exchange chromatography are likely to account for the failure of other labs to characterize the product.