Synexin protein is non-selective in its ability to increase Ca 2+-dependent aggregation of biological and artificial membranes

Abstract

Synexin, a soluble protein which increases the specificity of Ca 2+ to aggregate isolated bovine chromaffin granules was prepared from bovine adrenal medullary tissue by the method of Creutz, Pazoles and Pollard (J. Biol. Chem. 253 , 2858–2866, 1978). We also find that synexin increases both the initial rate and final amplitude of Ca 2+-promoted aggregation of granule membranes. This effect is Ca 2+-specific. However in contrast to Creutz et al , we find that synexin also potentiates aggregation of adrenal medulla and liver mitochondria and microsomes as well as phosphatidylserine vesicles. This lack of membrane specificity argues against the suggestion of Creutz et al that synexin specifically binds the granule to the plasma membrane prior to exocytosis in vivo .