INTERACTION OF RABBIT LIVER ANNEXINS WITH VARIOUS BIVALENT-METAL IONS- COMPETITION BETWEEN THE PROTEINS AND CHANGES IN THE ORDER OF ANNEXIN BINDING TO PHOSPHOLIPID-VESICLES

The interaction of a natural annexin mixture isolated from rabbit live r with liposomes prepared of soybean azolectin has been studied. With the limited number of accessible binding sites when liposomes can bind no more than 45% of the annexins added to the medium, the number patt ern of total annexin binding is very different in the presence of vari ous ions, especially in the presence of Ca2(+) and Sr2+, when distinct maxima and minima of binding are seen. The observed changes are due t o the competition of different annexins for the binding sites on lipos omes. The order of individual annexin binding was shown to change sign ificantly depending on the nature of the ion (Ca2+, Ba2+, Sr2+, Mn2+, Ni2+) present in the medium. The annexins are proposed to be just one of the constituents of a complex intracellular system interacting with various bivalent metal ions.