Interaction of annexins IV and VI with ATP: An alternative mechanism by which a cellular function of these calcium- and membrane-binding proteins is regulated

Abstract

Annexin VI from porcine liver can be photoaffinity-labeled with 8-azido-[γ- 32P]ATP in a concentration-dependent, saturable manner. The extent of labeling varied with the concentration of calcium. The dissociation constant for the nucleotide was found to be in the range reported for ATP-binding proteins. The ATP analog, 2′-(or 3′)- O-(2,4,6-trinitrophenyl)adenosine 5′-triphosphate, also bound to AnxVI, as indicated by shift in its fluorescence spectra in the presence of protein. Any significant 8-azido-ATP or TNP-ATP binding was not observed with AnxIV. ATP modulated the binding of AnxVI to erythrocyte membrane and increased the Ca 2+ concentration required for half-maximal binding of AnxVI to F-actin.