Abstract: Objective To derermine the affinity of site-specific labeled annexin V with 99mTc to phosphatidylserine (PS) exposed erythrocytes. Methods The annexin V fused with a metal chelating binding site was obtained from pichia pastoris culture and methanol induction expression. The annexin V was purified from the culture supernatant crude product by ultrafiltration. The annexin V was conjugated with 99mTc site-specifically with sodium glucoheptonic acid and SnCl2. The radioactive annexin V was added at wide range of concentration to determine its affinity to PS exposed erythrocytes. Results The calcium concentration at which half of the protein is bound to cells (EC50) is changed with varying ratio of protein to cells. The affinity was determined at lower protein to cells ratio as 33.4. Conclusion The annexin V expressed recombinantly in pichia pastoris show higher affinity to PS exposed erythrocytes.

Key words: annexin V, affinity, 99mTc, pichia pastoris, phosphatidylserine