THE RELATIONSHIP BETWEEN THE BINDING OF ATP AND CALCIUM TO ANNEXIN-IV- EFFECT OF NUCLEOTIDE ON THE CALCIUM-DEPENDENT INTERACTION OF ANNEXIN WITH PHOSPHATIDYLSERINE

With the use of ATP analogues, we have found that porcine liver annexi n (Anx) IV can be covalently labelled with 8-azido[gamma-P-32]ATP in t he presence of Ca2+ (K-d 4.2 mu M) and that the labelling is prevented by asolectin/cholesterol liposomes or chelation of calcium ions. On t he other hand, non-covalent binding of 2'-(or 3')-O-(2,4,6-trinitrophe nyl)adenosine 5'-triphosphate (TNP-ATP) to AnxIV occurs optimally in t he presence of liposomes and Ca2+ (K-d 7 mu M). These observations wer e further confirmed by the results of intrinsic fluorescence quenching of AnxIV with various nucleotides, suggesting the existence of a rela tionship between Ca2+-, phospholipid-and ATP-binding sites within the annexin molecule. The interaction of AnxIV with nucleotides does not s ignificantly affect its in vitro properties concerning the binding to phosphatidylserine (PS) monolayers.