The measurement of affinity of site-specific labeled annexin V with ~(99m)Tc by calcium titration / 基础医学与临床

ABSTRACT

Objective To derermine the affinity of site-specific labeled annexin V with ~(99m)Tc 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 uhrafihration.The annexin V was conjugated with ~(99m)Tc site-specifically through sodium glucoheptonic acid and SnCl_2.The radioactive annexin V was added 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 a low protein/cell ratio as 33.4.Conclusion The annexin V recombinantly expressed in Pichia Pastoris shows high affinity to PS exposed erythrocytes.