HIGHLY SENSITIVE AND STABLE PHOSPHATIDYLSERINE LIPOSOME AGGREGATION ASSAY FOR ANNEXINS

Annexins are a gene family of Ca2+-dependent membrane binding proteins which interact specifically with acidic phospholipids. We describe he re details of highly sensitive and precise assays for annexins I and V , utilizing turbidometric analysis of phosphatidylserine Liposome aggr egation. In the case of annexin I, the new assay is 7-fold more sensit ive than the conventional chromaffin granule aggregation assay in term s of threshold for detection and the rate of increase of initial absor bance is 15-fold greater. Annexin V, which binds but does not aggregat e liposomes, can be assayed on the basis of inhibition of Ca2+-depende nt liposome aggregation. Further comparative advantages of the assay i nclude lower expense and increased shelf life of the liposome reagent.